Friday, November 13, 2009

Ten Questions for HSF Committee - Question 2

Why wasn't a Phase I EELV HLV or similar HLV included in any options?

Is an affordable heavy lift vehicle possible? The Augustine Committee report’s cheapest heavy lift option is the Phase II EELV HLV, which delivers 75MT to LEO. Since by name this HLV variant is a "Phase II", obviously there is a Phase I. Phase I is a smaller EELV that delivers 40-50MT to LEO, depending on the specific EELV used.

The Committee's final report says

… the EELV-heritage super heavy is still larger than the Committee’s estimated smallest possible launcher to support exploration, which is in the range of 40 to 60 mt.

Thus a 40-50MT Phase I EELV HLV fits within the Committee's estimated smallest possible launcher range to support exploration. Why not simply implement Phase I then, and base exploration plans, or at least initial exploration plans, on that rocket for the larger exploration launches? Surely this would be cheaper and faster to develop than any of the report’s menu of heavy lift vehicles. Phase I is only a portion of Phase II, the cheapest HLV presented by the Committee in its options that don't fit the budget and enable beyond-LEO exploration at the same time.

There are advantages to the Phase I EELV HLV. Phase I would still allow a considerable amount of exploration, especially if combined with refueling, assembly, and docking in space. Although the most difficult and mass-intensive exploration missions may from one perspective be the most interesting and exotic ones, from another perspective the easier missions have a great deal of appeal in terms of economic potential. Perhaps it wouldn't be so bad if the Phase I EELV HLV causes us to dwell a bit longer at those destinations, developing their potential to the fullest.

It also wouldn't be bad if a smaller HLV encourages us to perfect our skills at refueling, ISRU, reusable space-only craft, frequent low-cost launch, docking, and assembly. All of these skills may find productive use outside NASA exploration. Enabling such capabilities may prove to be more important than NASA's actual exploration itself.

Phase I would also be more compatible with existing EELV production lines and infrastructure, and would be sized to have a greater chance than the larger HLVs to address realistic national security, commercial, and science needs outside NASA human spaceflight. I don't see national security, commercial, or science interests rushing to the head of the line with payloads in tow, eagerly waiting for a spot on a 75MT or greater HLV, and willing to pitch in some funding to make sure it happens.

Finally, if some day our exploration ambitions grow beyond Phase I, we could always continue to Phase II.

1 comment:

mp_meijering said...

Assembly isn't even needed and the refueling can be done with hypergolics, which is very mature technology. For efficiency reasons you would have to use L1/L2 rendez-vous for that. Transfer craft/landers would have to be refueled at L1/L2. Lagrange points are excellent staging points anyway and propulsive return to a Lagrange point is perfectly possible, even with hypergolics. This would make reusable craft possible right from the beginning. While this may not save much cost initially, it would allow you to trade construction costs for launch costs, which would give a bigger stimulus to the launch sector. It would also mean launch cost would be the main cost driver, so that improvements in launch costs could lead to higher mission rates. Use of Lagrange point depots also means that depots can be smaller. In particular, you wouldn't need an HLV to launch a depot. Interestingly, it would allow a lander to be used as a depot, making it unnecessary to spend extra money for development of a dedicated depot. You might still want that eventually, but it would be a nice-to-have not a must-have.