π Space
Is the satellite industry entering a “low-cost” era?

Sustainable fuel for satellite propulsion

Sophy Caulier, Independant journalist
On April 27th, 2021 |
4 min reading time
Ane Aanesland
Ane Aanesland
CEO and co-founder of ThrustMe
Key takeaways
  • Space pollution due to debris is a well-known problem for both experts in the sector and the general public.
  • To remedy this, the company ThrustMe has developed an electric engine designed to keep satellites in orbit as long as possible and to return them to Earth at the end of their life.
  • The chosen fuel is solid iodine, which reduces costs by a factor of 40! €1M euros would be enough to propel an entire constellation.

You co-found­ed ThrustMe in 2017 with Dmytro Rafal­skyi. What issues did you seek to resolve?

Ane Aanes­land. Our aim is to ensure that the space indus­try, which is under­go­ing major changes, becomes eco­nom­i­cal­ly and envi­ron­men­tal­ly sus­tain­able. To that end, we want to con­trol satel­lites bet­ter. We want to make sure that they can remain in posi­tion as long as pos­si­ble by avoid­ing col­li­sions and improv­ing their move­ments in orbit, as well as their ser­vice life.

The mul­ti­pli­ca­tion of con­stel­la­tions rais­es sev­er­al issues. To keep their cost afford­able, many micro- and nanosatel­lites do not have engines, and there­fore, are not autonomous. They are placed in low orbit, between 350 and 700 km, and at these alti­tudes one of two things will hap­pen. Either they grad­u­al­ly under­go fric­tion which mod­i­fies their orbit, pro­gres­sive­ly makes them descend and brings them into the atmos­phere where they burn; or they remain in orbit, where they die.

The lifes­pan of a satel­lite varies expo­nen­tial­ly depend­ing on the dis­tance of their orbit: 7 months at 300 km, more than 30 years at 700 km, and prob­a­bly 100 years at 1 000 km. Thus, satel­lites would have to be equipped with a propul­sion sys­tem in order to increase their lifes­pan in low alti­tudes and to descend those in high alti­tudes at the end of their ser­vice life. The prob­lem is that in the cur­rent sit­u­a­tion, propul­sion sys­tems con­sid­er­ably increase the cost and com­plex­i­ty of satel­lites. The ambi­tion of ThrustMe is to solve this issue.

What solu­tion did you come up with to rec­on­cile eco­nom­ic and envi­ron­men­tal challenges? 

We devel­oped a com­plete propul­sion sys­tem, which inte­grates the thruster, elec­tron­ics and fuel. It is an elec­tric thruster with sol­id iodine devel­oped for mini-satel­lites that weigh 10–100 kg/m. Three of these sys­tems were placed in orbit at the end of 2019 and in 2020 by the Chi­nese com­pa­ny Space­ty. Each were very dif­fer­ent: the first was a 6‑unit Cube­Sat (approx­i­mate­ly 12 kg), the sec­ond was a microsatel­lite weigh­ing around 50 kg, and the third a small satel­lite of 180 kg. We test­ed the dif­fer­ent fea­tures of our propul­sion sys­tems, and the results were extraordinary. 

How is your propul­sion tech­nol­o­gy dif­fer­ent from those that already exist? 

Cur­rent­ly, there are two types of propul­sion: chem­i­cal or elec­tric. The elec­tric sys­tem is rel­a­tive­ly new and only 20% of very big satel­lites are equipped with that. It is more effi­cient and eas­i­er to minia­turise than chem­i­cal propul­sion, which makes it per­fect for micro- and nanosatellites.

We chose iodine as the pro­pel­lant (the “fuel” of the thruster), because it is pos­si­ble to store it in sol­id form, and it only requires lit­tle heat to be sub­li­mat­ed into gas. In con­trast, xenon, used by most cur­rent elec­tric propul­sion sys­tems, must be stored under high pres­sure. Xenon is also a rare gas and in 5 to 10 years, the demand will be twice as high as the pro­duc­tion capacity.

Fur­ther­more, for a con­stel­la­tion of 800 to 1000 satel­lites, the cost of xenon is around €40M. SpaceX opt­ed for kryp­ton, which allowed them to divide by 3 the cost of the pro­pel­lant. But iodine divides this cost by 40. In oth­er words, only €1M are need­ed to pro­pel an entire con­stel­la­tion. It’s a real rev­o­lu­tion! We also demon­strat­ed in lab­o­ra­to­ry con­di­tions and direct­ly in space that iodine is more effi­cient than xenon at equal pow­er. This makes it pos­si­ble to keep the satel­lite in the right orbit or deor­bit it.

Do you have com­peti­tors on this technology? 

In the years 2015–2018, sev­er­al start-ups got involved in propul­sion, because there was a real lack of solu­tions on this area. So, yes, there is com­pe­ti­tion. Even the NASA tried to devel­op a solu­tion with man­u­fac­tur­ers, but iodine is not an easy sub­ject. It is cor­ro­sive. You need to know chem­istry, mate­ri­als sci­ence and so on. We devel­oped a solu­tion to trans­form iodine into gas then into plas­ma which, in addi­tion to its orig­i­nal­i­ty, also makes it pos­si­ble to reduce the weight and cost of the propul­sion sys­tem. It is not only the work of engi­neers. And here­in lies the strength of ThrustMe.

Could you be more specific?

We are a young and very small com­pa­ny com­pared to our com­pe­ti­tion. We only have 17 per­ma­nent staff and a few interns. But when deeptech com­pa­nies devel­op a prod­uct, they first run a proof of con­cept (PoC) and then see how to man­u­fac­ture the prod­uct. In our case, we con­sid­ered the man­u­fac­tur­ing of our propul­sion sys­tem from the very begin­ning. Of course, we have sci­en­tists, but we also have aero­space engi­neers, engi­neers in elec­tron­ics, etc. It was very impor­tant for us to hire engi­neers along with our sci­en­tists at the start of the com­pa­ny. We want­ed to con­tribute to the space rev­o­lu­tion which is cur­rent­ly under way. We want to change things and make the space indus­try more sustainable.

What is next for ThrustMe? 

At the begin­ning of 2020, we signed a first con­tract with the Euro­pean Space Agency (ESA), relat­ed to the ARTES pro­gram (Advanced Research in Telecom­mu­ni­ca­tions Sys­tems). It aims to solve the emerg­ing space-relat­ed chal­lenges asso­ci­at­ed with the rise of satel­lite con­stel­la­tions. We are also mak­ing sev­er­al sys­tems designed to equip a con­stel­la­tion for Earth obser­va­tion for a client.

More­over, we are con­duct­ing a mis­sion with the space agency of Nor­way on a satel­lite which will be launched at the begin­ning of 2022. The aim is to demon­strate col­li­sion avoid­ance with our elec­tric low-thrust thruster, the NPT30. It is the first mis­sion of this kind on a com­mer­cial satel­lite with an on-board high-pre­ci­sion GPS system.

Final­ly, we are also par­tic­i­pat­ing in a sci­en­tif­ic project of the INSPIRE pro­gram (Inter­na­tion­al Satel­lite Pro­gram in Research and Edu­ca­tion) with sev­er­al uni­ver­si­ties to study the upper ionos­phere, from 300 to 1000 km. The aim is to con­trol the descent of a satel­lite to 300 km and to main­tain it at this alti­tude to study cli­mate change.

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