Is the N-Prize Possible?

It has has been discussed on both the Space Fellowship site and even the N-Prize Forum that the N-Prize is somehow “impossible.”  This is false.

First, we must acknowledge historically that claims of impossibility have generally been met with embarrassing outcomes for the claimant; it is redundant to rehash the list of what was once thought impossible which we now take for granted, and I think such things are quite self-evident.

Second, we must acknowledge that the general claim of impossibility coveys with it knowledge of the entire set of what is possible – it is a term that no knowledgeable person should use as it points to a fundamental weakness in their thought process. While a well defined set may have instances of impossibility, an undefined or unknown set has no provisions to illuminate such a position. Thus, we defer to discuss probabilities and/or feasibilities, as all such metrics are really just an estimate.

With that, let's look at the N-Prize possibility/feasibility, and provide the rational behind Team LMR's entry into the competition.

In its most basic form, the N-Prize goal is to place a satellite into orbit. Well, we all know that is possible because it has been done already. Fine, let's move on...

Another aspect of the N-Prize is that the satellite is very small, 10g-20g. We know that such a small satellite is possible as well -- the physics demonstrate this, and there are pieces of space junk smaller than 20g that have found themselves in Earth orbit.

Another aspect of the N-Prize is that this small satellite must make 9 orbits around the Earth. We can calculate that this is on the edge of possibility with a reasonable 10g-20g satellite in LEO based on theoretical calculations (however, significantly more orbits than this do start pushing the physical limits).

Another aspect of the N-Prize is that that there must be a way to get the satellite into orbit; this can be any appropriate method. Traditionally, rockets have been used to launch payloads into orbit; there is no reason to think that a suitable rocket couldn't be used to launch a “small” payload into orbit.

As rockets scale down in size the challenges of reaching the required delta-V change somewhat due primarily to increased drag losses and the non-linear scaling aspects of advanced rocket machinery. Still, there is no theoretical/physical reason why a reasonably small launcher cannot be built to reach orbit. It may need a slightly greater overall delta-V to account for the increased drag losses given an endo-atmospheric launch strategy, but that in no way invalidates the possibility of such a launcher.

The rocket required to launch the 10g-20g payload can be any size that fits within the budget of £1000 (about $2000). This does not include any R&D cost – it is just per rocket materials and fabrication. Since a rocket this small would have very little material (other than propellant), the actual raw materials cost would by exceedingly low. Once designed, the fabrication costs would be equal to other types of mass produced devices with similar levels of machining complexity (in other words, quite low). Propellant costs would be even lower. So materials/fabrication cost is not an issue, and most of the budget, probably above 70%, would remain for the guidance and control systems.

The question of mechanical feasibility with respect to control authority, on this small scale, is certainly possible; the control accuracy is perhaps slightly greater than that required for large-scale RC aircraft.

The question of guidance and navigation, at this scale, is certainly possible in theory, but there are no concrete examples of it (as yet) and the hardware/software may not yet exist to implement at such a low cost – but that by no means makes it impossible. Certainly, if the budget was unconstrained this would not be an issue. It's just another engineering task, and there are no physical reasons to think that such a system can't be implemented within the budget limitation (in fact, LMR has already developed reasonable solutions to many of these GNC problems).

The question of developing control laws that can work at these lower Reynolds numbers while maintaining accurate estimates of attitude is not so much a question of possibility (all of us can “envision” a working system), but rather doing research and engineering an adequate system in this scale domain.

There are other odds and ends, but those above are the “big blocks” that would point to feasibility of the effort. The N-Prize does 'not' say place a 10kg satellite into orbit with a 1kg rocket; it conforms well to known physics and is more of an intellectual and engineering challenge than anything else.

The important point here is that nothing in this effort has been shown as fundamentally “impossible” or contrary to physics. Taken together, they do appear nearly impossible and so daunting, in fact, that the collective constraints place them at the current edge of feasibility in any rational person's estimation. But, that's what makes the project so worthwhile and exciting. It is one thing to do what “has” been done; it is completely another to do what “can” be done but few think is actually achievable. This is what really makes history – and this is what Team LMR intends to do.

~Sage