GAME-CHANGING TECHNOLOGIES IN ASTRONAUTICS (1/5)

At this time, 2025, I can say I am an old hand in Astronautics, having started in 2005, I have 20 years in the field and of course there are older hands, much older and thus respectable if some for their experience only.

The important factor here is that I’ve been witness of the transition from ‘Space 1.0’ to ‘Space 2.0’ and much of that transition has been thanks to game-changing technologies (GCT for short), of course many other factors have contributed, but space is about technology and science, without them, space remains an unreachable dream.

There are many of these GCTs, like the reusable rocket, the cubesat standard, miniaturized ion thrusters, the use of GPS in space, GS as a service (SatNOGS, AWS, etc), space tourism, space startups, space venture capital, etc, but I am going to center here in satellite technologies, basically small things that cast a big footprint.

Things like Micro HDRMs using shape memory alloys, Solar array hinges that can carry the current between panels eliminating the use of the nasty cables between them, Li-Poly batteries capable of charge and discharge at the same time, Single-card cubesat avionics that integrate EPS, Radio, OBC, solar manager and even deployables manager, Solar arrays with embedded antennas and even magnetorquers, Multi-HDRM controllers that can manage different HDRM techniques at once, High energy density batteries reaching up to 400W/kg, PCDUs that integrate batteries, EPS and solar array managers and even have their own OBC, MLIs that allow rad-hard level shielding for the whole spacecraft and even eliminate the dreaded thermal cycle, LASER communications for cubesats as small as 1U, Triple junction solar cells strings that cut the solar array manufacturing time by orders of magnitude, etc.

Describing all these technologies in one article will be extensive, so this will become a series of articles, each one addressing no more than 2, maybe 3 technologies at the time.

So let’s begin:

NANO HDRMS USING SHAPE MEMORY ALLOYS

While the use of shape memory alloys (SMA) is not new, and are routinely used in HDRM for micro and mini sized spacecrafts, these are big and bulky, even when some are really small, the micro-sized SMA HDRMs are an advance for their simplicity, strength, ease of use and virtual infallibility.

Of course, a nano size applies to the cubesat world and the breakthrough here comes from what normally the cubesat world uses as HDRM and that is the venerable thermal knife , (TK) a technique born in the early 1960s which is nothing more than a piece of nylon thread that is burned (cut) by a resistor, and it always works, that is why is so widely used, so what’s the problem with that?

The problem is that you have to rebuild the system each time you test it, meaning replacing the thread, sometimes replacing the resistor(s) and sometimes the board if you have done enough tests that you end up burning it. That is cumbersome to put it mildly and, in my opinion, frankly shameful to be sending a satellite into space with its solar arrays tied down by a piece of nylon, can we do better?

To do better, one has to beat the success rate of the TK and avoid its disadvantages and risks, while they are few, they are important:

-TK will fail without power, no power, no cut, no cut, no power because the solar arrays will not deploy, the typical catch-22, so your battery better be well charged when you try it in orbit.

-TK is so annoying to deal with during AIT that sometimes fails in orbit because somebody forgot to replace either the resistor or the thread.

So, what’s new? The Nano-HDRM from EXA, picture below:

A Nano- HDRM on a DMSA - 1U solar array for a 1U cubesat

It is a simple SMA bar holding down the solar arrays by tabs soldered on them, an enamel wire with the right number of turns is wrapped around it, when a small electric current is applied, the coil heats up until it warms the SMA bar up to the selected transition temperature and the bar straights out to its memory position, freeing the tabs and deploying the arrays, done.

What are the advantages of it?

• The first clear advantage over TK is that to try again, you only need to bend the bars with your hands (yes, with your hands) over the tabs and try again, no rebuilding, no burns, no re-soldering.

• The second clear and dramatic advantage is that they can work even without power, how? Because the sun eventually will heat the bars up to their transition temperature and they will release the arrays, this was observed in a 1U mission in 2013. It can take some more time, but eventually happens if for some reason you have a failure in your spacecraft that prevented the passing of the current to the coils

• Then there is the number of times they can be bent and re-bent, which is in the order of hundreds of times.

• And they are cheap

• You can even select the transition temperature of the bars as low as 40C and as high as 110C

  
  

And what are the cons?

• The speed of release depends on the strength of the current you use and the number of HDRMs you have on board, if you don’t have much power, a release can take as long as 45 seconds if you have 4 of these onboard while using only 2W

• As the wires are not burnt, you need to pay attention and disconnect the power feed once you have attained the release, if you don’t, you can have a serious power leak, but EXA offers a controller that automates the process and cuts the power once release have attained.

• The higher the transition temperature you select, the higher the power you will need to activate them

  
  

Not only they are used to release solar arrays, it also has been used as antennas, to deploy patch antennas and to deploy hatches like in the picture below:

A Nano- HDRM on a HTC01 hatch protecting delicate optics for a 12U cubesat

CURRENT-CARRYING SOLAR ARRAY HINGES

Well, you know, if you have a solar array made by a number of panels, you need to interconnect them for the current to reach the spacecraft, which is traditionally done using some form of cables between them and the cables will twist over and over again during AIT and will toast over time in orbit.

Those cables are normally made of multiple strands of silver over copper with a PTFE (Teflon) jacket, hooked by a multi-point connector, the fact is that for multi-year missions, the degradation of the cables start impacting in the yield of the solar arrays, affecting the expect mission time and bringing EOL (End-of-life) date quicker than expected. Also, is generally believed that the connectors do not impact the overall resistance in the circuit path, at least at BOL (Beginning-of-life) and that is generally true, but at the EOL they do, many people do not grasp the impact of ADCS operations over the connectors and the cables, by this meaning the jiggling of the panels when the spacecraft does an attitude change, it has been observed that over time it tends to loosen the connectors or worse, the base of the connector attached to the panels.

What can be better than a cable then? The answer is NO CABLES.

Enter the Current Carrying Hinges, from EXA: These are the hinges that provide structural support to the solar arrays and also carry the power from the panels, how?

The hinges are made of Aluminum alloy, others are made of pure copper and others made of a Beryllium-Copper alloy, all depending on the application and size of the solar panels, and the result is a solar array that has no cables, check the pictures below:

Beryllium- copper current carrying hinges in a 12U solar array Pure copper current carrying hinges in a 1U solar array

Aluminum alloy current carrying hinges in a 1 - meter- long micro satellite solar array

Many can say: ‘How is it possible to pass current without too much loss on a moving hinge?’ The answer lies in the clever design of the hinge and the electrical multipath redundancy built into them and the design of the solar array also, actually the transmission loss is near zero, we are talking about only 0.2 Ohms in 1.5 meters of transmission path, while using cables for that same length would yield a resistance of no less than 1 Ohm. And that is using Aluminum alloy, when pure copper or BeCu allow is used, the loss is so small that high precision equipment is needed to detect it, well in the range of 10-3-ohms. Now, you may say, ‘Ok, 1 Ohm is not so bad’ and that is right in you clean room at a balmy 21C, but once in orbit at scorching 100C or 120C that resistance can grow as much as 5 or even 10 Ohms depending on the length of the path from the spacecraft to the last panel in the array, so that means that:

Using cables: 48V@5A = 240W nominal yield

Resistance: 1 Ohm, then by V=I*R your voltage drop is 5V over 1.5 meters and therefore your real yield is 43V@5A = 215W, meaning you lost 25W because of the cables

Using CCHs: 48V@5A = 240W nominal yield

Resistance: 0.2 Ohm, then by V=I*R your voltage drop is 1V over 1.5 meters and therefore your real yield is 47V@5A = 235W, meaning you lost only 5W because of the hinges, That is 5 times less loss than using cables, let that sink in…

More to come, stay tuned.

Ronnie Nader

Chief Designer – EXA – rnader@exa.ec - ORCID: 0000-0002-1399-6973 - Scopus ID: 36125329900

Academician – Engineering Sciences – International Academy of Astronautics - IAA

Senior Member - Nuclear Propulsion Technical Committee – American Institute of Aeronautics and Astronautics - AIAA