Yes. Although difficult, there are no known physics which invalidate it.

Rockets work – and they work quite well. Eventually, we'll probably have better technology than rockets; but for now, rockets are the expedient method.

Both yes and no. Big picture, yes. However, we have several parallel development cycles with regards to the actual rocket designs. Recently, one has emerged as the probable winner. We are not ready to disclose our planned approaches, although we can state (which is probably already obvious) that all of our current directions include liquid-fed propulsion systems.

Our current focus is expendable but we are also considering reusable.

First (and especially in the category of the N-Prize we are most interested in), such techniques would (probably) push us over the allowed budget. But, even if we could make the budget in the reusable category, such techniques are somewhat questionable with regards to their advantages.

The purpose of all of these alternative methods (balloon, gun, plane, etc.) is to eliminate the major part of lower endo-atmospheric flight (i.e., the area in which the launch vehicle must fly through the densest part of the atmosphere). This is certainly a good idea in theory; balloons and planes do this rather efficiently, but rockets don't. So in essence, the objective of these methods is to substitute a “booster-stage” which might work better than a rocket.

Unfortunately for such techniques, the practical complexities typically outweigh the advantages, and historically, these alternative techniques have generally worked 'worse.' There are separate problems with each alternative method that rockets overcome naturally, but with small launchers such alternatives are indeed appearing more viable.

As an example, a very small launcher may find advantage on a balloon system, as flying a balloon is likely easier than building a first stage booster. On the other hand, a booster can loft the upper stages to altitudes greater than a balloon, and if one has the skill to build the upper stages, they probably have the skill to build the booster. Worse, though, is that people tend to underestimate the difficulties/details of launching from a balloon – balloons have their own peculiarities which are not trivial with respect to orbital insertion.

After examining the pros and cons of such systems, we've decided (at least at this juncture) to pursue a pure rocket approach. However, if we feel there is a compelling reason to change that direction towards an alternative “booster,” then we will certainly consider doing so.

We are considering both.

We have seriously considered SSTO, but are not ready to discuss the details of such a system. To note, it appears very unlikely that we will concentrate on an SSTO launcher exclusively.

While in theory SSTO is possible, the margin is exceptionally thin with regard to mass fraction. Two (or more) stages makes this task considerably easier and well within technological bounds for an inexpensive launcher.

Further, SSTO takes a penalty with regard to engine design. One cannot optimize bell nozzles for both endo and exo atmospheric flight – thus, the design has to be compromised if choosing SSTO with a non-altitude compensating nozzle. While in theory spike, plug, stepped bell, and other engines may overcome this, none have been shown as competitive in practice. Such alternative engines are generally heavier and are more difficult to design and cool; these complications nullify some of their theoretical advantages. Moreover, in a multi-stage design, the booster can be tailored for endo-atmospheric flight, and the upper-stages optimized for exo-atmospheric flight. So, not only can bell nozzles be used in a multi-stage system, but there is some optimization to be gained as well.

So far, the complexities of engineering an SSTO as a truly functional system when compared to a multi-stage launcher appear significantly greater. SSTO may in fact be less expensive, materials wise, than a multi-stage system. In fact, it may even be easier to build because there are fewer engines, no staging complications, etc. While these things are true, the level of engineering and precision required for a successful SSTO attempt, within these budget constraints, seems harder to achieve than with a multi-stage system.

In the interest of expediency, we opted to pursue those items which are largely common to both approaches. As we are planning to build several systems, such is not a problem at this time in our development cycle.

All are possibilities; we will likely opt for three stages if we choose a pressure-fed booster. Two stages (with the remote possibility of an SSTO) is probably the right number for this attempt with an advanced pump driven system.

Note that a pressure-fed system may require three stages as mass fractions and the lower pressure of the engines are unlikely to deliver the required performance to achieve it in two stages, unless advanced tanks and pressure vessels are used (which could be outside of budget). The trade-off is a simpler propellant feed system (pressure versus pump) as opposed to the likelihood of needing an additional stage.

In addition, our calculations indicate that a pressure-fed launcher would be several times heavier and physically larger than the pump-fed system; such will also be a factor in our decisions.

Certainly, drag losses are higher at these lower Reynolds numbers. The viscous forces are more significant, and the launcher needs to present a smaller scaled reference area and lower drag coefficient than its bigger counterparts. This generally means rockets with greater height/diameter ratios.

Our current plans include LOX and a light hydrocarbon; this may change during our hardware testing. Some of our approaches employ WFNA (white fuming nitric acid) as an alternative to the cryogenic LOX.