Sustainable fuel for satellite propulsion

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.