AnlaShok - 7/3/2007 6:44 AMWhy was a fourth Shuttle needed after the Challenger disaster? It was clear then that there would be not so many flights a year (not 60, not even 9), since no commercial satellite launches would be allowed. With five flights a year and an occasional DoD mission, wouldn't three Shuttles have been enough?
Gary - 7/3/2007 2:08 PMHL-20 would have been a new design and so it would have cost more to design, consult, build and test.Shuttle design was proven to work. Endeavour is basically built out of spare parts. Plus Columbia had a few other issues being heavier than the other Orbiters. This would mean that when the ISS got the go ahead only two shuttles could reach it (or one if either Discovery or Atlantis were down for OMM).
psloss - 7/3/2007 2:17 PMMaybe, but they flew more frequently than that in the period after Endeavour was delivered: 7 flights per calendar year between '93 and '97, inclusive. (With the 83/94 reflight in the middle of '97 adding an extra launch/landing.)After that, the ISS manifest started to dominate and the flight rate fluctuated...
Jim - 7/3/2007 2:27 PMThere was a thread on this already. HL-20 more practial for what? There was no mission for a HL-20.It was needed because orbiters were periodically taken out of the flight rotation for periods up to a year for inspections and maintanance
simonbp - 8/3/2007 8:47 AMBut lifting bodies have returned from orbital velocities (see SV-5D/PRIME and BOR-4), and their aerodynamics have been verified ad nauseum in hypersonic wind tunnels. The question is more why you want to use one in the first place...
Jim - 8/3/2007 9:21 AMNot true. those were only a few flights with limited data. Hypersonic wind tunnels do not operate at reentry velocities.
simonbp - 8/3/2007 6:50 PMQuoteJim - 8/3/2007 9:21 AMNot true. those were only a few flights with limited data. Hypersonic wind tunnels do not operate at reentry velocities.They don't need to be "reentry velocity", because they have an equivalent Reynolds number (look it up), and thus equivalent aerodynamics. Hypersonics is a 60+ year old science and not at all "unproven". The X-24 and HL-10 designs were tested extensively in exactly the same facilities (and by the same people) as Apollo and Shuttle, both of which seemed to work, and both of which are technically "lifting bodies" because their hypersonic lift/drag is greater than one. Heck, even the MSL entry aeroshell is technically a lifting body, to allow for a guided entry and thus more precise landing ellipse (exactly what lifting bodies were invented for). For more, look at "Wingless Flight" by Dale Reed, the guy basically invented the concept...Simon
Gary - 7/3/2007 10:01 PMthe shuttle was affordable with missions every two weeks as originally planned.