One clear problem with the Orbital Propellant Depots that are advocated by NASA's new plan is how to supply them. Rockets like the EELVs and the Falcon 9 have to little payload and are too expensive for the mission. I have advocated the development of a reusable rocket (and still do) but it does seem like that is not on the real world agenda for now.
So if we don't have a reusable system the alternative would be to have an economical system. I suggest for study the following. Build a rocket based on shuttle SRBs. The first stage would be a single four-segment SRB (just like the shuttle or the Ares 1-X), the second stage would be a two segment SRB, and the third would be a one segment stage.
As I understand it ATK has a lot more production capacity than used on the shuttle and be making large quantities of SRB segments one could achieve great economies of scale. We can even recover and reuse the first stages.
By the way, this is not an HLV proposal just to be clear. The real HLV would likely be too expensive for this mission. The final stages of the HLV could be refueled to launch payloads beyond LEO.
-- Edited by John on Sunday 18th of July 2010 05:16:01 AM
I need to remember to model before I post. A crude model I use shows that the above proposed rocket would fail to achieve LEO by at least 2100 ft/sec with ZERO payload!
At least this shows that I'm not prejudiced against SRBs or that I won't consider other ideas.
I it is difficult to rough out a design--I know, I have tried on many occasions. A good rule of thumb is a delta-V of 10,000 m/s for orbital veloticity: this includes losses from atmospheric drag, and 'gravity-turn' losses. Typically launch vehicles needs to achieve atleast 9600 m/s total mission velocity for orbital flight to reach an orbital velocity of about 7700 m/s. By choosing a more challenging 10,000 m/s it is slightly over conservative which will make certain things easier initially.
Once you have a concept roughed out, then you get into more detailed modelling of how much tankage you need to achieve a particular mission veloticy--which will now be a function of the desired payload you to send up....
Once you get the basic dimensions of the tanks down, then you focus more on the shape of the aeroshell. This allows you to estimate Coefficients of drag (especially if you have a CFD software pakage.) One you have the coefficients of drag then you can actually digitally simulate the thing to create a more realistic veloticity and trajectory profile, which allows you to zero in on a much more accurate estimate of the actual payload from required mission delta-V's.
I is an iterative process, and one that is necessarily complex, but it does rapidly get you into the ball park for what a vehicle can and can't do.
