MarCO (Mars Cube One)
Background: For a space mission intended to land on the surface of another planet for scientific exploration, the mission phase called EDL (Entry, Descent, and Landing) is the most risky of all mission phases. NASA has landed several spacecraft on the surface of Mars using different EDL technologies from Viking's entry from orbit to Curiosity's direct entry. For each case, the spacecraft arrives at high speed to the top of Martian atmosphere marking the end of the cruise phase and the start of EDL phase, where the speed is significantly reduced and a complex sequence of events follows until touch down. Due to the long round-trip light time between the spacecraft and ground controllers, mission teams rely on pre-programmed sequence execution without human interference and only monitor the resulting actions. Such monitoring requires near real-time communications from the landing vehicle to the ground stations either via a relay to an over-head orbiter, directly to Earth, or both. The DTE (Direct-To-Earth) method branches into two different techniques, telemetry and carrier-only.
When preparing for the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission EDL at Mars, originally planned to occur in 2016 and is currently planned for 2018, the JPL team was called upon to implement a DTE best-efforts approach to pick up the UHF carrier as was done with Phoenix, since the InSight spacecraft bus is inherited from the Phoenix bus. Work proceeded to make arrangements with large radio telescopes as has been done in the past. This time, however, new ideas and technologies have evolved since the Curiosity EDL to create a new concept. The advent of CubeSats commonly utilized at universities and launched for short duration mission in the Earth environment was a big factor. CubeSats, however, have never been flown in deep space or towards planetary targets. Among other limitations to achieve sufficiently distant deep space missions was the communications system. A CubeSat-sized transponder had not existed and X-band antennas as well as power amplifiers were also too big. However, JPL had breakthroughs in these areas in recent years. JPL prototyped a CubeSat-specific transponder called Iris initially intended to fly on the INSPIRE mission. This opened up the possibility of exploring a Mars CubeSat mission. Our formulation team studied the concept and documented a feasible spacecraft for management to secure funding. The mission is named MarCO (Mars Cube One).
When NASA launches its next mission on the journey to Mars – a stationary lander in 2018 – the flight will include two CubeSats. This will be the first time CubeSats have flown in deep space. If this flyby demonstration is successful, the technology will provide NASA the ability to quickly transmit status information about the main spacecraft after it lands on Mars. 3) 4) 5) 6) 7) 8)
The twin communications-relay CubeSats, being built by NASA/JPL (Jet Propulsion Laboratory), Pasadena, California, constitute a technology demonstration called Mars Cube One (MarCO). CubeSats are a class of spacecraft based on a standardized small size and modular use of off-the-shelf technologies. Many have been made by university students, and dozens have been launched into Earth orbit using extra payload mass available on launches of larger spacecraft.
MarCO's design is a 6U CubeSat with a stowed size of about 36.6 cm x 24.3 cm x 11.8 cm. MarCO will launch in May 2018 from Vandenberg Air Force Base, California on the same United Launch Alliance Atlas V rocket as NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) lander. Insight is NASA's first mission to understand the interior structure of the Red Planet. MarCO will fly by Mars while InSight is landing, in November2018.
Technology suppliers for MarCO include: Blue Canyon Technologies of Boulder, Colorado, for the attitude-control system; VACCO Industries of South El Monte, California, for the propulsion system; AstroDev of Ann Arbor, Michigan, for electronics; MMA Design LLC, also of Boulder, for solar arrays; and Tyvak NanoSatellite Systems Inc., a Terran Orbital Company in San Luis Obispo, California, for the CubeSat dispenser system.
C&DH (Command and Data Handling): AstroDev, LLC is providing an MSP430F2618 based Command and Data Handling board for the MarCO CubeSats. This board is based on modifications to the INSPIRE design, itself heritage from the RAX spacecraft. The C&DH has onboard non-volatile storage, a real-time clock, and cascaded watchdog system, and interfaces (SPI, I2C, UART, GPIO and RS-422) to all onboard subsystems.
A custom software, protos, was developed for INSPIRE and adapted for MarCO. This real-time operating system builds upon heritage from many previous JPL missions, yet fits within 128 kB of flash memory, and only 8 kB of RAM. The software allows for uploadable sequences, storage and transmission of real-time and historical telemetry, CCSDS packetizing for communications, and, most importantly, fault monitoring & response.
Power System: The MarCO CubeSats are powered by solar arrays, developed by MMA, LLC. These arrays fold to a single 3U panel for launch, but unfurl to reveal 42 solar cells, providing approximately 35 W of power (at 1AU). Each panel rotates upon deployment, but remains in a fixed position for the remainder of the flight.
The University of Michigan, under subcontract to AstroDev, provided the Electrical Power System for the MarCO CubeSats. The single set-point system allows of four channels of solar panel input, while regulating 5 V and 3.3 V buses (in addition to a battery bus). As MarCO utilizes a 3S4P Lithium Ion battery configuration, the power system was upgraded to an approximately 12 V battery bus. — The 18650B Lithium Ion batteries have been tested, screened, and assembled by the power systems section at JPL. A significant effort was made in matching cells and assuring good performance throughout the flight. These cells are protected by custom battery protection circuitry, and monitored by the C&DH subsystem.
RF communications: The heart of the MarCO CubeSats is the Iris V2 radio, customized for the MarCO mission to include a UHF receiver. This software-defined radio has up to 4 W RF output at X-band frequencies, is fully DSN compatible, and has 4 receive and 4 transmit ports. The Iris radio of JPL is capable of coherent 2-way Doppler, ranging, and DOR (Differential One-way Ranging) tones. To better accommodate mission communication and thermal requirements, the radio has an external solid-state power amplifier and low noise amplifier. In addition, the radio has been designed to be radiation tolerant. 9)
Figure 1: Illustration of the Iris V2 radio (image credit: JPL)
Each MarCO craft has a low-gain patch antenna for near-Earth communications with wide beamwidth, a medium gain patch array for safe-mode communications far from Earth, and a high-gain reflectarray antenna for high-speed data. The high gain antenna, paired with the Iris radio, can maintain an 8 kbit/s link from 1.05 AU. - In addition, a UHF loop antenna is deployed from the bottom of the spacecraft to receive data from the InSight lander during EDL (Entry, Descent, and Landing). 10)
Deep Space Transponder: The Iris radio was tested at the DSN Test Facility (DTF) to show RF compatibility and end-to-end dataflow. It is of utmost importance to provide final firmware/software within the radio to assure that measurements taken during the test may be trusted for flight operations, including receive threshold, power output, and expected data format. Much of this information is contained within the flightground interface control document. The flight mission operations center should be utilized for the end-to-end test to assure minimum risk to flight operations. 11)
The twin MarCO CubeSats are will be the first to travel into deep space, flying with NASA's InSight lander when it launches in May. Arriving at the Red Planet in November, these CubeSats will help provide realtime communication between the lander and NASA's DSN (Deep Space Network) here on Earth. They'll be working alongside the MRO (Mars Reconnaissance Orbiter), which has been orbiting the planet since 2006.
Figure 2: The MarCO CubeSats use a flat antenna called a reflectarray, the surface of which is patterned to mimic a parabolic dish, concentrating signals toward Earth (image credit: NASA/JPL)
Attitude Determination, Control, and Propulsion: Blue Canyon Technologies is providing the XACT (fleXible ADCS Cubesat Technology) attitude control unit, which includes a star tracker, gyro, coarse sun sensors, and 3-axis reaction wheels. Several modifications have been made to the base unit to include an additional coarse sun sensor and control of the thruster system. In addition, the software has been modified to account for deep space trajectories and related items.
The onboard micro propulsion system, built by Vacco, contains 8 thrusters – 4 canted for attitude control, and 4 for TCMs (Trajectory Correction Maneuvers). Vacco's single tank design houses all electronics, valves, and propellant. The propellant is R-236FA, a cold-gas propellant often used in fire extinguishers. MarCO uses a cold gas propulsion system with a capability of 755 Ns, providing in excess of 40 m/s of TCM ΔV, enough for what is needed for a Mars-bound mission. The thrusters will operate for trajectory adjustments and for desaturating the reaction wheels. -The XACT system commands the thrusters to fire both for reaction wheel desaturation, as well as for the TCMs. For safety, power control of the propulsion system is maintained by the C&DH.
Figure 3: The Vacco micro propulsion system for MarCO (image credit: Vacco) 12)
Structure, Thermal and Harnessing: Both the structure and harnessing (cabling and interface boards) have been designed by engineers at JPL. The structure maintains compatibility with the 6U CubeSat standard.
The MarCO thermal design includes two discrete radiators, thermal blanketing, onboard heaters, and a myriad of temperature sensors throughout the vehicles. As the craft will significantly change their distance from the sun, the project has carefully balanced radiator sizing against subsystem "on" time, power usage, and replacement heater considerations. With the tightest thermal constraints, the batteries have a dedicated radiator to isolate them from larger swings in the overall vehicle temperature.
Figure 4: MarCO flight system overview (image credit: NASA/JPL)
Figure 5: Engineers for NASA's MarCO technology analyze the small craft in development as part of NASA's next mission to Mars (image credit: NASA/JPL-Caltech)
Figure 6: The full-scale mock-up of NASA's MarCO CubeSat held by Farah Alibay, a systems engineer for the technology demonstration, is dwarfed by the one-half-scale model of NASA's Mars Reconnaissance Orbiter behind her (image credit: NASA/JPL)
Figure 7: Illustration of one of the twin MarCO spacecraft with some key components labeled. Front cover is left out to show some internal components. Antennas and solar arrays are in deployed configuration (image credit: NASA/JPL)
Launch: The two experimental MarCO CubeSats were launched on 5 May 2018 (11:05 UTC) as secondary payloads of the NASA InSight mission to Planet Mars. The Atlas V-401 vehicle of ULA was the launch vehicle and the launch site was VAFB, CA. 13) 14) 15)
The spring-loaded CubeSat deployment system for MarCO is on the aft bulkhead carrier of the Centaur upper stage of InSight's Atlas V launch vehicle. That is near the base of the Centaur, not inside the fairing that encloses the main spacecraft. At launch and until the Centaur upper stage separates from the first stage of the Atlas V, the aft bulkhead carrier is sheltered within an inter-stage adaptor between the launch vehicle and the second, or upper, stages. 16)
After the Centaur upper stage has released the InSight spacecraft on course toward Mars, it will do a short roll, then release MarCO-A, roll 180 degrees further and release MarCO-B.
Orbit of MarCO: The two CubeSats will separate from the Atlas V booster after launch and travel along their own trajectories to the Red Planet. After release from the launch vehicle, MarCO's first challenges are to deploy two radio antennas and two solar panels. The high-gain, X-band antenna is a flat panel engineered to direct radio waves the way a parabolic dish antenna does. MarCO will be navigated to Mars independently of the InSight spacecraft, with its own course adjustments on the way.
Figure 8: Mars InSight & MarCO - First Interplanetary Cubesat Mission (video credit: NASA/JPL, Caltech)
• February 5, 2019: Before the pair of briefcase-sized spacecraft known collectively as MarCO launched last year, their success was measured by survival: If they were able to operate in deep space at all, they would be pushing the limits of experimental technology. 17)
- Now well past Mars, the daring twins seem to have reached their limit. It's been over a month since engineers have heard from MarCO, which followed NASA's InSight to the Red Planet. At this time, the mission team considers it unlikely they'll be heard from again.
- MarCO (Mars Cube One) was the first interplanetary mission to use a class of mini-spacecraft called CubeSats. The MarCOs - nicknamed EVE and WALL-E, after characters from a Pixar film - served as communications relays during InSight's landing, beaming back data at each stage of its descent to the Martian surface in near-real time, along with InSight's first image. WALL-E sent back stunning images of Mars as well, while EVE performed some simple radio science.
- All of this was achieved with experimental technology that cost a fraction of what most space missions do: $18.5 million provided by NASA's Jet Propulsion Laboratory in Pasadena, California, which built the CubeSats.
- WALL-E was last heard from on Dec. 29; EVE, on Jan. 4. Based on trajectory calculations, WALL-E is currently more than 1 million miles (1.6 million kilometers) past Mars; EVE is farther, almost 2 million miles (3.2 million kilometers) past Mars.
- The mission team has several theories for why they haven't been able to contact the pair. WALL-E has a leaky thruster. Attitude-control issues could be causing them to wobble and lose the ability to send and receive commands. The brightness sensors that allow the CubeSats to stay pointed at the Sun and recharge their batteries could be another factor. The MarCOs are in orbit around the Sun and will only get farther away as February wears on. The farther they are, the more precisely they need to point their antennas to communicate with Earth.
- The MarCOs won't start moving toward the Sun again until this summer. The team will reattempt to contact the CubeSats at that time, though it's anyone's guess whether their batteries and other parts will last that long.
- Even if they're never revived, the team considers MarCO a spectacular success.
- "This mission was always about pushing the limits of miniaturized technology and seeing just how far it could take us," said Andy Klesh, the mission's chief engineer at JPL. "We've put a stake in the ground. Future CubeSats might go even farther."
- A number of the critical spare parts for each MarCO will be used in other CubeSat missions. That includes their experimental radios, antennas and propulsion systems. Several of these systems were provided by commercial vendors, making it easier for other CubeSats to use them as well.
- More small spacecraft are on the way. NASA is set to launch a variety of new CubeSats in coming years.
- "There's big potential in these small packages," said John Baker, the MarCO program manager at JPL. "CubeSats - part of a larger group of spacecraft called SmallSats - are a new platform for space exploration that is affordable to more than just government agencies."
• November 27, 2018: NASA's MarCO mission was built to see whether two experimental, briefcase-sized spacecraft could survive the trip to deep space, and the two CubeSats proved more than able. After cruising along behind NASA's InSight for seven months, they successfully relayed data back down to Earth from the lander during its descent to the Martian surface on Monday, Nov. 26. 18)
Figure 9: MarCO-B took this image of Mars from about 4,700 miles (6,000 km) away during its flyby of the Red Planet on Nov. 26, 2018. MarCO-B was flying by Mars with its twin, MarCO-A, to attempt to serve as communications relays for NASA's InSight spacecraft as it landed on Mars (image credit: NASA/JPL-Caltech)
- MarCO-A and MarCO-B (nicknamed "EVE" and "WALL-E") used experimental radios and antennas, providing an alternate way for engineers to monitor the landing. The CubeSats provided information to InSight's landing team in just 8 minutes - the time it took for radio signals to travel from Mars to Earth. That was much faster than waiting on NASA's Mars orbiters, which weren't positioned to be able to observe the entire event and send data back to Earth immediately.
- "WALL-E and EVE performed just as we expected them to," said MarCO chief engineer Andy Klesh of NASA's Jet Propulsion Laboratory in Pasadena, California, which built the CubeSats. "They were an excellent test of how CubeSats can serve as 'tag-alongs' on future missions, giving engineers up-to-the-minute feedback during a landing."
- Landing on Mars is exceptionally difficult: Before InSight, only about 40 percent of all attempts by various nations had succeeded. Even if a spacecraft doesn't survive landing, having a "black box" - or a pair of them, as with MarCO - to record the event can help engineers design better landing technology.
- Neither of the MarCO CubeSats carry science instruments, but that didn't stop the team from testing whether future CubeSats could perform useful science at Mars. As MarCO-A flew by, it conducted some impromptu radio science, transmitting signals through the edge of Mars' atmosphere. Interference from the Martian atmosphere changes the signal when received on Earth, allowing scientists to determine how much atmosphere is present and, to some degree, what it's made of.
- "CubeSats have incredible potential to carry cameras and science instruments out to deep space," said John Baker, JPL's program manager for small spacecraft. "They'll never replace the more capable spacecraft NASA is best known for developing. But they're low-cost ride-alongs that can allow us to explore in new ways."
- As a bonus, some consumer-grade cameras aboard MarCO provided "drive-by" images as the CubeSats sailed past Mars. MarCO-B was programmed to turn so that it could image the planet in a sequence of shots as it approached Mars (before launch, MarCO-A's cameras were found to be either non-functioning or too blurry to use).
- After the landing, MarCO-B turned backward to take a farewell shot of the Red Planet. It also attempted to snap some photos of Mars' moons, Phobos and Deimos.
- "WALL-E sent some great postcards from Mars!" said Cody Colley of JPL, MarCO's mission manager, who led the work to program each CubeSat to take images. "It's been exciting to see the view from almost 1,000 miles (1,600 km) above the surface."
- With the mission's objectives reached, the MarCO team will spend the next couple of weeks collecting additional data on each CubeSat. Of interest will be how much fuel is left in each CubeSat and detailed analyses of how their relay capability performed.
• One of the twin MarCO CubeSats snapped this image of Mars on Oct. 3 - the first image of the Red Planet ever produced by this class of tiny, low-cost spacecraft. The two CubeSats are officially called MarCO-A and MarCO-B but nicknamed "EVE" and "Wall-E" by their engineering team. 19)
Figure 10: One of NASA's twin MarCO spacecraft took this image (annotated) of Mars on October 2 — the first time a CubeSat, a kind of low-cost, briefcase-sized spacecraft — has done so (image credit: NASA/JPL-Caltech)
- A wide-angle camera on top of MarCO-B produced the image as a test of exposure settings. The MarCO mission, led by NASA's Jet Propulsion Laboratory in Pasadena, California, hopes to produce more images as the CubeSats approach Mars ahead of Nov. 26. That's when they'll demonstrate their communications capabilities while NASA's InSight spacecraft attempts to land on the Red Planet. (The InSight mission won't rely on them, however; NASA's Mars orbiters will be relaying the spacecraft's data back to Earth.)
- This image was taken from a distance of roughly 8 million miles (12.8 million km) from Mars. The MarCOs are "chasing" Mars, which is a moving target as it orbits the Sun. In order to be in place for InSight's landing, the CubeSats have to travel roughly 53 million miles (85 million km). They have already traveled 248 million miles (399 million km).
- MarCO-B's wide-angle camera looks straight out from the deck of the CubeSat. Parts related to the spacecraft's high-gain antenna are visible on either side of the image. Mars appears as a small red dot at the right of the image.
- To take the image, the MarCO team had to program the CubeSat to rotate in space so that the deck of its boxy "body" was pointing at Mars. After several test images, they were excited to see that clear, red pinprick.
- "We've been waiting six months to get to Mars," said Cody Colley, MarCO's mission manager at JPL. "The cruise phase of the mission is always difficult, so you take all the small wins when they come. Finally seeing the planet is definitely a big win for the team."
• August 2018: Mission Concept of Operations. 20)
- Early planned mission operations consisted of spacecraft checkout and deployment of panels and antennas. Within several weeks of launch, both MarCO's were scheduled to perform a TCM (Trajectory Correction Maneuver), steering the flight path toward Mars, and removing the launch vehicle bias. Follow-on TCMs (up to 4 additional) throughout the mission allow for minor correction of the final flyby trajectory.
- Following a 6.5-month cruise, and arriving at Mars on November 26, 2018, the MarCO spacecraft are planned to relay telemetry data back from the InSight lander as it proceeds through EDL (Entry, Descent and Landing) to landing on Mars. The Mars Reconnaissance Orbiter will simultaneously record the broad InSight signal (including telemetry data) and will subsequently send this to Earth. During EDL, a UHF carrier tone will be received by Earth, providing limited insight into descent events. Though the MarCO spacecraft are not required for InSight mission success, their presence and operations allow for near-real-time telemetry downlink and health monitoring of the EDL process. - After EDL data relay, the MarCO spacecraft will complete their demonstration objectives and primary mission by mid-December.
- Deployment: To avoid launch vehicle or primary spacecraft (InSight) interference, each MarCO was inhibited from opening panels or powering on the radio until verification of sun-light measured on the vehicle and at least 5 minutes following dispenser deployment. After this delay, the spacecraft energized each solar array burn-wire circuit three times (for redundancy), and subsequently turned on the attitude control system to despin and orient the spacecraft. Soon after, a scheduled "beep" mode was entered, where the radio began a short duration (5 min) receive-transmit sequence, allowing the ground to receive the first data from orbit. As the spacecraft was designed to enter a sun-pointing spin, it was unclear if the antennas would be pointed correctly during this time. Several minutes later, a second 7-minute "beep" was scheduled.
- Figure 11 best illustrates actual onboard events through annotation of battery bus voltage. Significant drops occur when large loads (such as energizing burn-wires) are applied. As part of the solar arrays are still exposed when stowed, initial tumble rates are also provided.
- Both MarCO-A and MarCO-B successfully completed the initial deployment sequence. MarCO-A had a tumble rate of less than 0.5º/s, while -B was slightly faster at approximately 2º/s. Each spacecraft remained warm from launch, with onboard internal temperatures around 18ºC. Solar panels were successfully actuated upon the first burn-circuit excitation, and initial telemetry indicates they fully deployed.
- Each spacecraft also communicated with ground control during each beep opportunity, providing a first look at the deployment sequence and spacecraft health. Batteries were nearly fully charged at deployment, and subsequent looks indicated a power-positive state. Wheel rates remained low, the star tracker showed good expected performance, and the spacecraft remained in a stable attitude.
Figure 11: Bus voltage from MarCO-B following launch vehicle separation, annotated with mission events (image credit: NASA/JPL-Caltech)
- Trajectory Correction Maneuvers: MarCO is pioneering meeting planetary protection requirements within the framework of a CubeSat mission. Classified as a Planetary Protection Category III flyby mission, the project is required to address both impact constraints for launch vehicle elements and the potential for contaminating InSight. Meeting these requirements by adopting the contamination analysis and control architecture typically applied to Mars missions would limit the benefits of the low-cost, highly-adaptable CubeSat paradigm. Instead, a strategy comprising bioassays of specific hardware, conservative bioburden estimation, and worst-case vehicle breakup and burnup analyses was employed to ensure Planetary Protection compliance.
- Yet as the launch vehicle did not (and could not) meet the stringent cleanliness requirements of a Mars impacter, the mission was specifically launched to off-point from Mars. TCMs are used to re-align a spacecraft's trajectory towards its destination – in this case, to establish MarCO on a heliocentric trajectory that was coincident with a Mars flyby at the time of InSight's EDL.
- To achieve this goal, up to five TCMs are planned, spread throughout the mission, and biased late to allow for final small adjustment. Small maneuvers early in the mission can account for large changes at the end, so early uncertainty is corrected once additional navigation tracking has been accomplished. To maintain appropriate distance between InSight and the two MarCO spacecraft, the MarCO TCM-1 sequence was performed after InSight, essentially providing the primary spacecraft "first-pick" of preferred flight path. Each MarCO's TCM was designed to best align for Mars flyby, to maintain the flight path within DSN coverage of InSight (which allows for multiple-spacecraft-per-aperture reception of MarCO data when InSight is being tracked), and to account for any uncertainty in thruster performance.
- The MarCO spacecraft each have an onboard cold-gas propulsion system, capable of achieving greater than 30 m/s of ΔV. Early characterization of this system, both during desaturation maneuvers and a blow-down sequence (to empty the plenum) showed good performance, though slow compared to traditional "burns". Rather, the spacecraft perform closer to a low-thrust system, with multiple firings happening over minutes to achieve a desired ΔV. This has an inherent advantage, where tracking can occur between various stages, providing additional position estimation accuracy.
- The navigation team at JPL has made use of both ranging and Doppler tracking of the MarCO spacecraft to provide a position estimate. Later in the mission, ΔDOR (Delta-Differential One-way Ranging) tracking will be tested to refine this estimate. Over multiple days of simultaneous data downlink and ranging, each spacecraft's position was refined.
- In summary, the MarCO spacecraft have now entered cruise phase and are performing well. Initial deployment showed two healthy vehicles at minimal attitude rates, ready for spacecraft checkout. Following checkout, the first TCM maneuver aligned both spacecraft toward Mars, even though MarCO-B continues to account for an ongoing slight propellant leak through a thruster. After a 6.5 month cruise, the MarCO spacecraft will be ready to support InSight during EDL.
- As a technology demonstration mission, the MarCO spacecraft are proving the capability of a low-cost mission to survive and thrive in the deep space environment, and training scientists and engineers in the sometimes difficult world of operations. The limited energy budget available to MarCO causes for short communication passes and careful planning for activities. This can affect how quickly a TCM can occur, how to plan for the downlink of historical data, and how often the thruster system can be utilized. By the time MarCO reaches Mars, the spacecraft will have reached distances half a million times further than most CubeSats to date.
- MarCO – the first interplanetary CubeSats – is blazing a trail for follow-on missions, and many additional lessons will come in the journey ahead.
• June 1, 2018: NASA has achieved a first for the class of tiny spacecraft known as CubeSats, which are opening new access to space. 21)
- Over the past week, two CubeSats called MarCO-A and MarCO-B have been firing their propulsion systems to guide themselves toward Mars. This process, called a trajectory correction maneuver, allows a spacecraft to refine its path to Mars following launch. Both CubeSats successfully completed this maneuver; NASA's InSight spacecraft just completed the same process on May 22.
- While MarCO-A corrected its course to Mars relatively smoothly, MarCO-B faced some unexpected challenges. Its maneuver was smaller due to a leaky thruster valve that engineers have been monitoring for the past several weeks. The leak creates small trajectory changes on its own. Engineers have factored in these nudges so that MarCO-B can still perform a trajectory correction maneuver. It will take several more weeks of tracking to refine these nudges so that MarCO-B can follow InSight on its cruise through space.
- "We're cautiously optimistic that MarCO-B can follow MarCO-A," said Joel Krajewski of JPL, MarCO's project manager. "But we wanted to take more time to understand the underlying issues before attempting the next course-correction maneuver."
- Once the MarCO team has analyzed data, they'll know the size of follow-on maneuvers. Several more course corrections will be needed to reach the Red Planet.
• May 15, 2018: NASA's Voyager 1 took a classic portrait of Earth from several billion miles away in 1990. Now a class of tiny, boxy spacecraft, known as CubeSats, have just taken their own version of a "pale blue dot" image, capturing Earth and its moon in one shot. 22)
- NASA set a new distance record for CubeSats on 8 May when a pair of CubeSats called MarCO (Mars Cube One), reached 1 million kilometers from Earth. One of the CubeSats, called MarCO-B (and affectionately known as "Wall-E" to the MarCO team), used a fisheye camera to snap its first photo on 9 May (Figure 12). That photo is part of the process used by the engineering team to confirm the spacecraft's high-gain antenna has properly unfolded.
- As a bonus, it captured Earth and its moon as tiny specks floating in space. "Consider it our homage to Voyager," said Andy Klesh, MarCO's chief engineer at NASA's Jet Propulsion Laboratory, Pasadena, California. JPL built the CubeSats and leads the MarCO mission. "CubeSats have never gone this far into space before, so it's a big milestone. Both our CubeSats are healthy and functioning properly. We're looking forward to seeing them travel even farther."
- If the MarCO CubeSats make the entire journey to Mars, they will attempt to relay data about InSight back to Earth as the lander enters the Martian atmosphere and lands. MarCO will not collect any science, but are intended purely as a technology demonstration. They could serve as a pathfinder for future CubeSat missions.
Figure 12: The first (annotated) image captured by the MarCO-B CubeSat on 9 May 2018, showing both the CubeSat's unfolded high-gain antenna at right, and the Earth and its moon in the center (image credit: NASA/JPL-Caltech)
• May 05, 2018: NASA has received radio signals indicating that the first-ever CubeSats headed to deep space are alive and well. The first signal was received at 12:15 p.m. PST (3:15 p.m. EST) today; the second at 1:58 p.m. PST (4:58 p.m. EST). Engineers will now be performing a series of checks before both CubeSats enter their cruise to deep space. 23) 24)
After Separation (Ref. 16)
If all goes according to plan, within about 10 minutes after separation from the Centaur, each MarCO will begin to deploy its solar panels. Each MarCO generates electric power with a pair of photovoltaic panels, and each panel has an area of about 30 cm x 30 cm. Combined, these panels can provide each spacecraft about 35 watts when near Earth and 17 watts when near Mars. The power system also will use rechargeable lithium-ion battery cells, crucial for operations when spacecraft orientation for communication prevents the solar arrays from facing the Sun.
After the solar arrays are deployed, the MarCO control team will acquire radio contact with each CubeSat, one at a time, via NASA's Deep Space Network. Early tasks will be to establish that the spacecraft are healthy, stable and commandable.
During the flight to Mars, the MarCO twins will each attempt to deploy a high-gain X-band antenna that is a flat "reflectarray" panel engineered to direct radio waves the way a parabolic dish antenna does. This will allow MarCO to transmit data to Earth from as far away as Mars without needing much power, if the spacecraft works as planned. Two smaller X-band antennas on each spacecraft — one low-gain and one medium-gain — work without needing to be deployed. These will serve for transmissions earlier in the flight and will also receive radioed commands from Earth.
The other deployed antenna is for the MarCO ultra-high frequency (UHF) radio receiver. InSight will be transmitting in UHF during its descent through the Martian atmosphere and from the surface of Mars. Both of the deployed antennas on each MarCO will be in fixed positions after deployment, with the high-gain antenna and UHF antenna facing different directions 90 degrees apart. The MarCOs will also test new technology using a softball-size radio, called "Iris." This radio provides both UHF (receive only) and X-band (receive and transmit) functions capable of immediately relaying information received over UHF, at 8 kilobits per second.
A color wide-field engineering camera on each MarCO will be used to confirm high-gain antenna deployment. The wide-field camera has a 138-degree diagonal field of view. Each MarCO also carries a color narrow-field camera with a 6.8-degree diagonal field of view pointed in the direction of the UHF antenna (the opposite direction from the high-gain antenna). Both cameras can produce images 752 by 480 pixels in resolution.
The team will navigate MarCO-A and MarCO-B separately to Mars with course adjustments along the way. The first of five opportunities for MarCO trajectory correction maneuvers will come about a week after launch.
Each MarCO's attitude-control system combines a star tracker, Sun sensors, gyroscopes and three-axis reaction wheels for monitoring and adjusting orientation. Accelerating a reaction wheel rotates the spacecraft in the opposite direction from the direction the wheel is spinning.
Figure 13: An artist's rendering of the twin MarCO spacecraft as they fly through deep space. The MarCOs will be the first CubeSats — a kind of modular, mini-satellite — attempting to fly to another planet. They're designed to fly along behind NASA's InSight lander on its cruise to Mars. If they make the journey, they will test a relay of data about InSight's entry, descent and landing back to Earth. Though InSight's mission will not depend on the success of the MarCOs, they will be a test of how CubeSats can be used in deep space (image credit: NASA/JPL)
Figure 14: NASA's two small MarCO CubeSats will be flying past Mars in November 2018 just as NASA's next Mars lander, InSight, is descending through the Martian atmosphere and landing on the surface. MarCO (Mars Cube One), will provide an experimental communications relay to inform Earth quickly about the landing (image credit: NASA/JPL)
"MarCO is an experimental capability that has been added to the InSight mission, but is not needed for mission success," said Jim Green, director of NASA's planetary science division at the agency's headquarters in Washington. "MarCO will fly independently to Mars."
During InSight's EDL (Entry, Descent and Landing) operations on Nov. 26, 2018, the lander will transmit information in the UHF radio band to NASA's MRO (Mars Reconnaissance Orbiter ) flying overhead. MRO will forward EDL information to Earth using a radio frequency in the X-band, but cannot simultaneously receive information over one band while transmitting on another. Confirmation of a successful landing could be received by the orbiter more than an hour before it's relayed to Earth.
MarCO's radio is about softball-size and provides both UHF (receive only) and X-band (receive and transmit) functions capable of immediately relaying information received over UHF.
Each MarCO will maintain an orientation with the UHF antenna pointed down toward InSight as it lands on Mars, and the high-gain X-band antenna pointed back toward Earth. In this orientation, the solar panels will not face the Sun, so MarCO will be operating on battery power. InSight will be transmitting its status information at 8 kbit/s over UHF. Each MarCO will attempt to receive that data stream, format it and relay it Earthward in near-real-time to NASA's Deep Space Network (Figure 16). Since MarCO adds formatting information, as well as a small amount of spacecraft information, to the datastream, the delay is expected to increase as more data are sent from InSight. The delay, however, is not expected to be more than a few minutes. Earth will be oriented so that the information relayed via MarCO will go to the Madrid, Spain, station of the Deep Space Network, from which it will be routed to the InSight mission operations team.
Figure 15: MarCO concept of operations (image credit: NASA/JPL)
Figure 16: MarCO will relay data from InSight to Earth during InSight's descent through Mars' atmosphere and touchdown on the surface. NASA's Mars Reconnaissance Orbiter will also receive these data from InSight (image credit: NASA/JPL)
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).