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.