Ross Tierney and Antonio Maia ("simcosmos") have brought Baker/Zubrin Ares up to date and called it the DIRECT. This booster is characterized by:
- Has 2 RS-68 engines under the core; standard version plans to have regenerative engines
- The homework isn't complete, but it plans to use the existing ET hydrogen tank, interstage, and aft LOX dome, with a minor redesign of the ET hydrogen aft dome to accommodate the thrust structure and manifold interfaces. The new LOX tank will be smaller (RS-68 has a lower mixture ratio) and an ellipsoidal forward bulkhead similar to the LOX tank's aft bulkhead will be used. BZ Ares is very similar, but has a LOX tank of the same volume as on the existing ET.
- It uses standard 4 segment RSRM boosters, just like the Shuttle already does.
- The CLV variant doesn't have an upper stage, but the CaLV variant, with the same lower stages, uses an EDS upper stage almost identical to that of the BZ Ares with my proposed mods (common bulkhead tank.)
Performance of the standard CLV is 70,900kg to LEO.
TASS2 analysis of the BZ Ares has revealed that its performance does not significantly exceed this. TASS2 implements the following, most of which were not implemented in our BZ Ares model and the version of Orbiter it was originally drawn up for (IIRC it was either 020217 or 030303.)
- Underexpansion of nozzle gasses at low altitude
- Atmospheric drag
- 103.5sec full blast SRB (i.e. no thrust bucket; I believe our ZB Ares runs full thrust for 124sec, which would have the side effect of increasing Isp well beyond that attainable for solid propulsion.)
- Other differences are slightly conservative, and become liberal (and outrageously so) only once the booster reaches circular velocity.
At ERV payload, TASS2 estimates that BZ Ares is about 1200m/s slower than it is in Orbiter at 1/2 staging.
Send me an email to aftercolumbia at gmail dot com if you would like a copy of TASS2-ZBAres.xls; it is too big to put in the Yahoo Group file section. If you can't take a big attachment, tell me, and I'll trim it down so it can be restored using fill commands. I'll be converting it to DIRECT shortly in terms of my contribution to OMDP, but it'll be a while before I can get back to OMDP...other projects call.