GAME-CHANGING TECHNOLOGIES IN ASTRONAUTICS (2/5)

In this chapter (2/5):

• Li-Poly batteries capable of charge and discharge at the same time (SCC)

• Single-card cubesat avionics that integrate EPS, Radio, OBC, solar manager, deployables manager and even LASER comms

BATTERIES THAT CAN CHARGE AND DISCHARGE SIMULTANEOUSLY (SCC)

To many people this is unheard of; to others is the natural way to do batteries.

The truth is that in astronautics this is mostly unheard of, while in the rest of the reality, this is the natural way to do batteries, or does not your phone keeps working while you are charging it? Well, that is not the way it is done traditionally in space technology, why?

It is mostly because the type of battery and the way the BMS (Battery Management System) and EPS (Electrical Power Supply) systems are traditionally done, but that does not mean it cannot be done. In fact, EXA has done it like that since 2011 and never had any problem; on the contrary, the benefits are huge compared with the traditional way to do batteries in astronautics.

No every type of battery can do this, like NiCad, NiMH, and even some Li-ion, the ones that can do this trick are like the ones in your phone or tablet or Notebook computer, the Lithium-Polymer ones, but that is not the end of the story, you need an special EPS/BMS architecture to support that kind of trick. But OK, what is the big deal here, why is this so desirable?

Let’s check the Pros:

• Li-Poly batteries have a finite number of charging cycles, normally between 700 and 1000, by charging and discharging simultaneously. you never complete a cycle, making the battery duration span much longer, in the years range, some missions sporting this technology have been observed to work beyond the 10-year range.

• With SCC, your energy pool onboard multiplies by 1.5 at least. Why? Because in illumination it is not only your batteries powering the spacecraft: it is also the power of your solar arrays, so when you use this technology you should add the power of the solar arrays to the batteries, contrary to what you do when you don’t have SCC, because in that case your solar arrays are only dedicated to charge your batteries and they do not participate in powering the spacecraft.

• You enter the eclipse cycle with your batteries charged at 70% to 90% even after full use in illumination due to the SCC dual function by leaning the discharge of the batteries into the solar arrays.

• Using SCC, you don’t have to stop your mission to charge

• When you use SCC, the batteries warm up building up heat that when you enter eclipse and the temperature of the spacecraft goes down to -80 outside, that heat will be radiated back to your spacecraft interior, warming up your electronics and eliminating the radical temperature swings inside the spacecraft that we use to call thermal cycle, the overall result is that your spacecraft interior temperature stabilizes around 10 to 15 degrees over time. Very comfy.

• These batteries cannot explode.

• They can be serialized for higher voltages while still be charged in parallel.

• The supported temperature range is extreme: they can be submerged in Liquid Nitrogen at -180C and keep collecting charge and working after going back to +20C and on the high side they can sustain up to 80C and keep working, although doing this regularly will shorten their lifetime.

Now, let’s check the Cons:

• Using Li-Poly batteries carries risk, as they are pouch batteries, they must be physically constrained to avoid swelling or they can leak, but not explode.

• The lead time of these batteries is long, why? Because the best Li-Poly batteries can last for years, even decades, but the defective ones are very insidious and they can start swelling spontaneously after a few weeks or even months and therefore manufacturers have to ‘mature’ the cells by observing them for long periods of time.

• Cells have to be well isolated by their BMS or the failure of one can lead to the failure of all

Many batteries have their own onboard BMS and even onboard redundant charging circuitry like the BA06, BA07 and BA08 from SmallSat.Market:

BA07 and BA08 SCC batteries

SINGLE-CARD CUBESAT AVIONICS

In the cubesat world, everything is done stacking PCB boards and sharing one stackable connector, like:

• 1 card for the OBC

• 1 card for the radio

• 1 card for the batteries

• 1 card for the ADCS subsystem

• 1 card for the EPS

• 1 card (each) for the payload(s)

And you end up with a lot of cards occupying a lot of space in your cubesat and a 1U size may not be enough so you have to use a 2U or 3U size and your launch costs multiple by 2 or 3, Can we do better? The answer is Yes.

The ICEPS single card avionics from EXA is unique in the world, is the only product that combines:

• On Board Computer (OBC) ARM9 dual core 733MHz processor

• Software Defined Radio managing from 70MHz to 6GHz

• EPS capable of handling up to 100W with 3 power rails at 3V3, 5V and 12V (or more)

• Solar manager UMPPT capable of handling up to 4 solar arrays at 16V@2A each

• LASER communications up to 10MBps

• Deployables manager up to 8 deployable devices

• BMS system with charger up to 2A

• Capable of managing up to 8 payload cards

• Onboard solid state, rad-hard storage up to 512 GB

Only the ADCS system is not included, but available as a separate board, but then, the whole system, including the battery, only occupies 0.2U of space!, making possible cheaper and more powerful 1U missions, even for 3U systems where you can easily fit a decent resolution EO camera using ICEPS, It has been used even in 6U missions up to date.

This is how ICEPS look besides a 1U cubesat, again: all 8 main subsystems packed in one single card:

And now, take a look at how does a traditional cubesat looks against how a cubesat looks using ICEPS:

A traditional cubesat 1U stack A single card avionics stack using ICEPS with 25W

battery and ADCS card

Will say no more, images speak louder than words and one image is worth a thousand words, 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 Aerona utics and Astronautics - AIAA