Mars Cube One
Mars Cube One (or MarCO) is a Mars flyby mission that was launched on 5 May 2018 alongside NASA's InSight Mars lander mission. It consists of two nanospacecraft, MarCO-A and MarCO-B, that were able to provide a real-time communications link to Earth for InSight during its entry, descent, and landing (EDL) on 26 November 2018 - when InSight was out of line of sight from the Earth. Both are of the 6U CubeSat format, and the mission is a test of new miniaturized communications and navigation technologies. These are the first CubeSats designed to operate beyond Earth orbit, and aside from telecommunications they also tested CubeSats' endurance in deep space.
Rendering of the two MarCO spacecraft fully deployed
|Mission type||Communications relay test|
|Spacecraft type||6U CubeSat|
|Launch mass||13.5 kg (30 lb) each|
|Start of mission|
|Launch date||5 May 2018, 11:05 UTC|
|Rocket||Atlas V 401|
|Launch site||Vandenberg Air Force Base SLC-3E|
|Contractor||United Launch Alliance|
|Flyby of Mars|
|Closest approach||26 November 2018, 19:52:59UTC|
|Distance||3,500 km (2,200 mi)|
The InSight lander re-transmitted its telemetry data during the landing, which demonstrated the new relay system and technology for future use in missions to other Solar System bodies. This provided an alternative to the orbiters for relaying information and achieved a technology development threshold.
Mars Cube One is the first spacecraft built to the CubeSat form to operate beyond Earth orbit for a deep space mission. CubeSats are made of small components that are desirable for multiple reasons, including low cost of construction, quick development, simple systems, and ease of deployment to low Earth orbit. They have been used for many research purposes, including: biological endeavors, mapping missions, etc. CubeSat technology was developed by California Polytechnic University and Stanford University, with the purpose of quick and easy projects that would allow students to make use of the technology. They are often packaged as part of the payload for a larger mission, making them even more cost effective.
The two Mars Cube One spacecraft are identical and officially called MarCO-A and MarCO-B and were launched together for redundancy; they were nicknamed by JPL engineers as WALL-E and EVE in reference to the main characters in the animated film WALL-E. The MarCo mission cost is $18.5 million USD.
JPL's MarCO engineers view the Mars flyby as a technology demonstration that could lead to many more low-cost, targeted small satellite missions outside of Earth's orbit. While keeping an eye on the performance of the MarCO mission, NASA has proposed spending more money on CubeSats as a complement to multi-billion-dollar projects which sometimes face years of delay.
The launch of Mars Cube One was managed by NASA's Launch Services Program. The launch was originally scheduled for 4 March 2016 on an Atlas V 401, but the mission was postponed to 5 May 2018 after a major test failure of an InSight scientific instrument. The Atlas V rocket launched the spacecraft together with InSight, then the two MarCO separated soon after launch to fly their own trajectory to Mars in order to test CubeSats' endurance and navigation in deep space.
During the cruise phase, the two spacecraft were kept about 10,000 km (6,200 mi) away from InSight at either flank for safety, and the distance was reduced as the three spacecraft approached Mars. The closest flyby distance to Mars was 3,500 km (2,200 mi).
The primary mission of MarCO is to test new miniaturized communication and navigation technologies. They were able to provide real-time communication relay while the InSight lander was in the entry, descent, landing phase.
The MarCO spacecraft were launched as a pair for redundancy, and flew at either side of InSight. While there are a large number of CubeSats around Earth, Mars Cube One is the first CubeSat mission to go beyond Earth orbit. This allowed for collection of unique data outside of the Earth's atmosphere and orbit. In addition to serving as communications relays, they also tested the CubeSat components' endurance and navigation capabilities in deep space. Instead of waiting several hours for the information to relay back to Earth directly from the InSight lander, MarCO thus relayed EDL-critical data 8 minutes after the completion of the landing. The information sent to Earth included an image from InSight of the Martian surface right after the lander touched down.
Without the MarCO CubeSats, InSight would relay the flight information to the Mars Reconnaissance Orbiter (MRO) which does not transmit information as quickly. Seeing the already-present difficulty in communicating with ground control during especially risky situations, various teams set out to revise the way in which data is relayed back to Earth. Previous missions would send data directly to Earth after landing, or to nearby orbiters, which would then relay the information. Future missions may no longer choose to rely on these methods, since CubeSats may be able to improve data relay in real time, as well as reduce the overall mission cost.
Design and componentsEdit
The design includes two communication-relay CubeSats, built by NASA's Jet Propulsion Laboratory, which are of the 6U specification (10×20×30 cm). A limiting factor to the development of CubeSats is that all necessary components must fit within the frame of the satellite. It must contain the antenna, avionics to control the satellite, a propulsion system, power, and payload.
On board the two CubeSats is an ultra-high frequency (UHF) antenna which is circularly polarized. The EDL information from InSight was transmitted through the UHF band at 8 kbit/s to the CubeSats, and was simultaneously retransmitted at an X band frequency at 8 kbit/s to Earth. MarCO used a deployable solar panel for power, but because of the limitations in solar panel efficiency, the power for the X-band frequency can only be about 5 watts.
In order for the CubeSats to be able to relay information, they need to have a high gain antenna (HGA) which is reliable, meets the mass specs, has low complexity, and is affordable to build. A high gain antenna is one that has a focused, narrow radiowave beam width (directional antenna). Three possible types of antennas were assessed: a standard microstrip patch antenna, a reflectarray, and a mesh reflector. With the small, flat, size required for the CubeSats, the reflectarray antenna type met all of the mission needs. The components of a reflectarray HGA are three folded panels, a root hinge which connects the wings to the body of the CubeSat, four wing hinges, and a burn wire release mechanism. The antenna panels must be able to withstand a varying degree of temperature changes throughout the mission as well as vibrations throughout deployment. MarCO relayed EDL-critical data 8 minutes after the completion of the landing.
The propulsion system features eight cold gas thrusters which control the trajectory, and a reaction control system to adjust their attitude (orientation). On the way to the correct transmission destination, the propulsion system made five small corrections to ensure the two small spacecraft were on the correct trajectory. Small changes in trajectory early on in the mission's deployment not only saved fuel but also the space which any extra fuel would have taken up, thus conserving volume for other important components inside the spacecraft. MarCO-B (WALL-E) has been leaking propellant gas almost since liftoff, but has enough to complete its mission.
Having completed their primary mission, the small spacecraft shall continue in their elliptical orbits around the Sun. Engineers expect them to keep working for a couple weeks after they pass Mars orbit, depending on how long their propellant and electronics last.
Each MarCO carries a softball-sized radio used to communicate with the ground using X-band, to receive data from InSight using UHF, and to collect tracking measurements for navigation. Their attitude control system is equipped with a star tracker that is used to determine the attitude of the spacecraft. In addition, each MarCO carries a miniature wide-angle camera that is used to verify deployments and to capture outreach images.
Similar missions beyond Earth orbitEdit
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