Strained Mars data relay capabilities possible in 2020s
As InSight begins its journey to Mars, communications between the Red Planet and Earth could face a potential gap in data relay capabilities over the next decade. As its current fleet of orbiting spacecraft age with no new NASA orbiter under development, SpaceFlight Insider investigated the options available to maintain data relay capabilities with spacecraft on the surface into the 2020s.
Communicating with spacecraft on the surface of Mars is no easy task. A range of limiting factors including the planet’s rotation, the number of spacecraft at Mars, and the weak signals transmitted from surface spacecraft can make consistent and rapid direct communication from the surface of Mars to Earth a challenge. To facilitate a more consistent and reliable flow of data between spacecraft and their operators on Earth, data relay utilizing spacecraft orbiting Mars has been consistently employed since the early 2000s.
The venerable Mars Global Surveyor (MGS) and Mars Odyssey spacecraft were the first to employ data relay capabilities in the modern era of Mars exploration. They operated as relays for the twin Mars Exploration Rover missions until the arrival of the Mars Reconnaissance Orbiter (MRO) in 2006.
MGS entered into a safe mode in November 2006 and NASA later declared the mission over in January 2007 after the space agency failed to reestablish contact with the aging orbiter. The 12-year-old MRO and 17-year-old Odyssey have served as the primary data relays for Mars surface missions since.
The value of using orbiting spacecraft as relays has proven invaluable. From an engineering standpoint, it allows for a reduction in total spacecraft mass for landers by lowering the equipment requirements for communication payloads. For mission operators, it allows them to plan more intensive schedules for landers and rovers by reducing the amount of time spent sending and receiving data, a task accomplished by limited transmissions during windows when orbiting spacecraft are overhead.
Project scientists and researchers also see a benefit in the increased volume of science that can be returned from the surface thanks to the reduction in time spent communicating with Earth and increase in science activities.
Where is the replacement?
Until the end of 2016, proposals were being funded to explore options for the development of a replacement telecommunications and science orbiter to be dispatched to Mars during the 2022 launch window. Mission proposals for the Mars 2022 orbiter (also called the Next Mars Orbiter, or NeMO) were varied but centered around several common elements. The primary design elements for NeMO would include solar electric ion drive propulsion and the deployment of broadband optical (laser) communication equipment.
Ion drive propulsion could serve as a demonstration of the technology in a Mars exploration setting as well as provide an opportunity to serve as a return vehicle to transport samples during the proposed Mars Sample Return mission. Additionally, instrumentation for NeMO would be built on legacy hardware from MRO and would ensure continuity in the high resolution imagery and remote sensing observations that have been collected at Mars over the past two decades.
However, funding for NeMO has been largely phased out in favor of directing limited funds towards the development of the Mars Sample Return mission. Mars Sample Return has the primary objective of fetching samples that scientists plan to collect and cache using the Mars 2020 rover currently under development. The current Planetary Science Decadal Survey has listed the flagship sample return mission as the primary objective for NASA’s Mars program in the 2020s, along with requisite funding. The existing fleet of orbiting spacecraft at Mars, while aging, are in generally good health meaning the postponement of a new orbiter will require careful management of existing orbital assets into the next decade.
When asked about NASA’s plans to rely on current spacecraft, MRO Project Scientist Dr. Richard Zurek remains optimistic about the continuity of relay capabilities into the 2020s. Dr. Zurek also serves on NASA’s Mars Exploration Program Analysis Group (MEPAG) and is currently the Chief Scientist for the Mars Program Office at the Jet Propulsion Laboratory (JPL).
“There is some concern that the assets we have are aging, but the program is looking at options to fill the gap,” Dr. Zurek said of MEPAG’s evaluation of existing orbital assets. “Hopefully future resources will include MRO. We’re not counting on Odyssey [over the long term], but we’re also looking to move MAVEN into a more suitable orbit in the future.”
Options going forward
From the perspective of age alone, Mars Odyssey has vastly surpassed the lifespan of its prime mission which ended in August 2004. Despite occasionally entering into a protective safe mode, the failure of one of its three main flywheels in 2012 stands as perhaps its largest equipment malfunction to date. The flywheel failure required a fourth spare to be brought into service and the spacecraft has been operating nominally since. Scientists have previously stated that barring a major equipment failure, they predict Odyssey has enough fuel that it can continue operations through 2025.
Assuming that Odyssey ceases operations before other spacecraft, MRO would need to handle data relay for both current and planned missions to the surface going forward. According to Dr. Zurek, MRO has enough fuel to accomplish this through at least 2027. However, additional spacecraft at Mars can be called into service to help provide additional support and redundancy.
While the inclination of their orbits are not ideal to support the current data relay work load, the ExoMars Trace Gas Orbiter and Mars Atmospheric and Volatile Evolution Mission (MAVEN) can provide limited support if required. Both spacecraft carry Electra UHF transmitters similar to those on MRO enabling them to communicate with spacecraft on the surface. An early test of MAVEN’s relay capabilities in 2014 demonstrated it’s effectiveness in data relay with a transfer of 550 gigabits – or over half a terabyte – of information sent from Curiosity during a single pass.
Plans are on the books to adjust the orbits of ExoMars and MAVEN once their primary science mission objectives have been met in the coming years in order to be better positioned to assist with data relay in the future. They do not carry enough fuel to adjust their inclinations and so the consistency of their relay services would not be as frequent as Odyssey or MRO.
New techniques are being developed to help with data relay in the future. The InSight mission will for the first time test the deployment and viability of using cubesats at Mars to relay information during the entry, descent, and landing (EDL) phase of the mission. Data relayed during EDL provides critical engineering data on the health of the spacecraft and can be useful for engineers in diagnosing sources of error should the landing attempt fail. However their use for prolonged data relay is limited—due in part to the energy requirements involved as well as their inability to carry fuel and navigation equipment required to keep the spacecraft oriented.
“Cubesats are ideal for short bursts of data, but not ideal for larger datasets or datarates,” said Dr. Zurek. “Other communications systems are being talked about including optical communications that are possible for increasing datarates down the road.”
In terms of managing existing assets, the MRO team is already applying strategies to manage MRO’s navigation equipment, power resources, and fuel reserves going forward. In March, mission operators directed the spacecraft to adopt an all-stellar navigation method to preserve the onboard inertial measurement units (IMU’s) for major spacecraft adjustments only. The all-stellar method uses on-board cameras to track stars as reference points to ensure the spacecraft is pointed at Mars and can be utilized indefinitely barring a failure of any of the cameras.
To conserve MRO’s power resources, the mission team is conditioning the batteries to hold more charge by gradually adjusting the spacecraft’s orbit so that it spends less time in the planet’s shadow. When asked about the power requirements for data relay and being able to continue with the current pace of science observations, Dr. Zurek indicated that MRO does not need a lot of power for relay capabilities.
“There should be enough power from solar panels to help power the data relay as well as science capabilities,” Zurek said. “The issue is primarily focused on making sure the spacecraft does not draw low voltage and to make sure the batteries are in good shape.”
With the power and navigation resources managed wisely, fuel becomes the primary constraining factor the team can control. Nearly 200 kg (440 lbs) of fuel remain onboard for use during course corrections and other orbital adjustments, which Dr. Zurek estimates can sustain the craft through at least 2027.
All options considered, MRO is likely to remain the workhorse of data relay going forward into the 2020s, and it’s an assignment that Dr. Zurek and the MRO team embraces. In the meantime, the development of a new orbiter will remain on NASA’s wish list for future budget requests. Barring a new influx of funding for the project, a new telecommunications orbiter may not be sent to Mars until the second half of the 2020s.
Paul is currently a graduate student in Space and Planetary Sciences at the University of Akransas in Fayetteville. He grew up in the Kansas City area and developed an interest in space at a young age at the start of the twin Mars Exploration Rover missions in 2003. He began his studies in aerospace engineering before switching over to geology at Wichita State University where he earned a Bachelor of Science in 2013. After working as an environmental geologist for a civil engineering firm, he began his graduate studies in 2016 and is actively working towards a PhD that will focus on the surficial processes of Mars. He also participated in a 2-week simluation at The Mars Society's Mars Desert Research Station in 2014 and remains involved in analogue mission studies today. Paul has been interested in science outreach and communication over the years which in the past included maintaining a personal blog on space exploration from high school through his undergraduate career and in recent years he has given talks at schools and other organizations over the topics of geology and space. He is excited to bring his experience as a geologist and scientist to the Spaceflight Insider team writing primarily on space science topics.