CubeSats: exploring other planets on a budget

“Any man who can hitch the length and breadth of the galaxy, rough it, slum it, struggle against terrible odds, win through, and still knows where his towel is is clearly a man to be reckoned with.”

– Douglas Adams

Exploring the solar system is absurdly expensive. Even a single mission, such as NASA’s US$675 million InSight probe to Mars, scheduled to launch in May 2018, would eclipse the total science budget of most nations. But with tiny, hitchhiking satellites called CubeSats, there may finally be a way to explore other planets on a shoestring.

Tagging along on that InSight mission will be two CubeSats – small, boxy satellites the size of a carry-on suitcase. Built by NASA’s Jet Propulsion Laboratory, these Mars Cube One (or MarCO) probes will be the first CubeSats to voyage to another planet. If they pull off their US$13 million mission – peanuts compared with any previous interplanetary mission – MarCO could lead to a shift in how we explore the solar system, even opening the doors to smaller nations to stake a claim. Space travel finally has an economy-class fare.

CubeSats were originally designed as a training tool, so university students could design and build satellites in the timeline of a semester. The basic idea was to cram the instrumentation into a standard template: a cube with 10 cm sides. 

Almost 20 years on, more than 500 cubesats have been launched successfully into orbit, with another 600 launches planned for 2017 alone. CubeSats have turned into the great leveller of modern space exploration, achievable within the budget of schools, universities, or even crowdfunding campaigns.

Stacking cubes together delivers the flexibility to make larger, sophisticated CubeSats such as LightSail-1, which hoisted a 32 m2 solar sail in 2015. But so far, no CubeSat has ever left low earth orbit, which is within 160 km of the Earth’s surface.{%recommended 1195%}

The MarCO mission requires two CubeSats to fly, by themselves, across more than 200 million km of deep space during their six-and-a-half-month mission. To survive in deep space, they’ll need a serious upgrade on the standard model.

Each MarCO is a six-unit CubeSat stuffed with two deployable solar panels, two antennas and a radio the size of a tennisball. Special mini-thrusters, using the same kind of propellant as in some fire extinguishers, will help the MarCOs make course corrections during the journey. To survive the bombardment of cosmic rays and solar wind, they’ll use robust, radiation-resistant electronics.

MarCO’s job is to receive data from the InSight lander during its so-called “seven minutes of terror” as it punches through the Martian atmosphere on its way to becoming the first seismometer on Mars. During this critical period of atmospheric entry and landing, InSight can’t communicate with Earth directly, so MarCO will relay the data. While this job is not mission-critical for Insight, it is the perfect demonstration of the feasibility of CubeSats far from Earth orbit.

If successful, MarCO could alter the way we explore the solar system generally. NASA envisions launching swarms of CubeSats, each carrying a single instrument or performing a single task. Each becomes a low-cost, highly specialised probe, rather than a jack-of-multiple-trades as with conventional space probes.

Steven Hobbs, a planetary scientist at the University of New South Wales, says sending a bunch of low-cost missions might end up giving more bang for buck compared with typical, multi-tonne probes that are very difficult to build and “that only superpowers could afford.” Another possibility is to send sacrificial CubeSats to the solar system’s most hellish places, such as the surface of Venus, the plumes of Europa or inside the volcanoes of Io.

At least a dozen other deep space CubeSat missions are in the works. Even before MarCO, the INSPIRE  project could be the first CubeSat to escape Earth orbit, some time in 2017. It will carry two instruments: a magnetometer to measure magnetic fields – useful for probing the the solar wind in fine detail – and a simple camera so it can orient itself by the stars. 

In 2018 NASA will send its new Orion spacecraft around the Moon and back, with 13 CubeSats tagging along for the ride. After the Orion capsule’s separation from its upper stage, the CubeSats will be be ejected to take on a range of missions: searching for ice on the moon, studying how yeast deal with space radiation, scouting near Earth for asteroids, measuring space weather and more.

Hitchhiking could be the new way to see the solar system. No towel required.

Specifications

Name: Mars Cube One (MarCO)
Destination: Martian orbit
Mission cost: 
(MarCO) US$13 million,  
(Insight) US$425 million
Launch Date: 20 May 2018
Mars Arrival: 26 November 2018
Dimensions (while stowed): 36.6 x 24.3 x 4.6 x 11.8 cm.
Mass: 14 kg

Unfolding

MarCO will deploy from the Atlas V rocket carrying InSight one week after launch. MarCO’s first challenge as an independent spacecraft will be to unfold its two wing-like solar panels, and its flat-packed communications systems.

Solar Arrays

Each solar array contains 42 individual solar cells and provides 35 W of power – about enough to power a modern laptop computer.

UHF Antenna

This small ultra high frequency (UHF) antenna is capable of receiving data from InSight at 8 kbit/s. To ensure a crisp signal, during InSight’s “seven minutes of terror” this antenna will point directly at Mars. 

Cold Gas Thrusters

Each MarCO is equipped with four axial and four attitude control thrusters, each capable of 25 mN of thrust (equivalent to the weight of two paperclips on your palm). That may not sound like much, but it’s enough to make the minor course corrections needed on the 6.5-month-long journey to Mars.

High Gain Reflectarray

This flat panel relays X-band signals at 8 kbit/s to the Deep Space Network dishes back on Earth. During the InSight landing, MarCO will rotate so the reflectarray can transmit direct to home base.

X-Band transponder

This transponder converts the UHF signal received from InSight to the X-band signal (in the microwave range) for sending back to Earth.