The ESAS report is always an interesting read:
5.3.2.5 CEV Split Versus Single Volume
A considerable amount of time was spent analyzing the advantages and disadvantages of a
CEV split versus single volume. Separating the CEV volume into a CM used primarily for
ascent and entry and a mission module that could be sized and outfitted for each particular
mission has operational advantages depending on the mission to be supported. Also, separation
of the mission module with the SM after the Earth deorbit burn provides the lightest and
smallest reentry shape.
The difficulty in minimizing the ascent/entry volume of the vehicle became a driving factor
because this volume must accommodate a maximum crew of six for the Mars return mission.
Once the ascent/entry volume for six was determined, all other DRM crew sizes by definition
will fit in this volume. A CEV sized for the six-crew DRM is the minimum size for the ascent/
entry module.
The study found a single volume, which is less complex from a build-and-integrate standpoint,
to be more mass-efficient and volume-efficient for a given mass. A larger single-volume vehicle
also has lower entry heating and g’s as a result of a larger surface area, and thereby lower ballistic
coefficient, than a smaller ascent/entry split volume. A mission module was determined to
not be required for the ISS and the Mars return DRMs and was of limited value to the lunar
DRM, if the single volume is large enough, and the CEV is not taken all the way to the lunar
surface.
5.3.1.2 Blunt Bodies Versus Slender Bodies Trade
The shape study trade was initiated between major vehicle classes. The primary classes
considered were capsules (blunt bodies), slender bodies, lifting bodies, and winged vehicles.
Winged bodies and lifting bodies (such as X–38, X–24, HL–10, etc.) were eliminated at the
outset due to several factors, including: (1) the extreme heating (especially on empennages)
these would encounter on lunar return entries, (2) the additional development time required
due to multiple control surfaces, and (3) the increased mass associated with wings, fins, and
control surfaces which are huge liabilities in that they must be carried to the Moon and back
simply for use on entry. Thus, the trade space involved capsules versus slender bodies. It was
planned that, after a desirable class of vehicle was selected, the shape would be optimized
within that class.
The ESAS report is always an interesting read:
5.3.2.5 CEV Split Versus Single Volume
A considerable amount of time was spent analyzing the advantages and disadvantages of a
CEV split versus single volume. Separating the CEV volume into a CM used primarily for
ascent and entry and a mission module that could be sized and outfitted for each particular
mission has operational advantages depending on the mission to be supported. Also, separation
of the mission module with the SM after the Earth deorbit burn provides the lightest and
smallest reentry shape.
The difficulty in minimizing the ascent/entry volume of the vehicle became a driving factor
because this volume must accommodate a maximum crew of six for the Mars return mission.
Once the ascent/entry volume for six was determined, all other DRM crew sizes by definition
will fit in this volume. A CEV sized for the six-crew DRM is the minimum size for the ascent/
entry module.
The study found a single volume, which is less complex from a build-and-integrate standpoint,
to be more mass-efficient and volume-efficient for a given mass. A larger single-volume vehicle
also has lower entry heating and g’s as a result of a larger surface area, and thereby lower ballistic
coefficient, than a smaller ascent/entry split volume. A mission module was determined to
not be required for the ISS and the Mars return DRMs and was of limited value to the lunar
DRM, if the single volume is large enough, and the CEV is not taken all the way to the lunar
surface.
5.3.1.2 Blunt Bodies Versus Slender Bodies Trade
The shape study trade was initiated between major vehicle classes. The primary classes
considered were capsules (blunt bodies), slender bodies, lifting bodies, and winged vehicles.
Winged bodies and lifting bodies (such as X–38, X–24, HL–10, etc.) were eliminated at the
outset due to several factors, including: (1) the extreme heating (especially on empennages)
these would encounter on lunar return entries, (2) the additional development time required
due to multiple control surfaces, and (3) the increased mass associated with wings, fins, and
control surfaces which are huge liabilities in that they must be carried to the Moon and back
simply for use on entry. Thus, the trade space involved capsules versus slender bodies. It was
planned that, after a desirable class of vehicle was selected, the shape would be optimized
within that class.
So I guess with all their "gifted" foresight in selection everything is working out just fine then...
There's also the fact that if an escape tower fails to jettison, the crew dies. If the escape system is needed, say, on one in 1000 flights, then it harms crew safety as much as it helps if there is a 0.1% chance of failing to jettison.
Except the Russians have needed to use the LES twice and it worked fine both times.
Only once (Soyuz T-10), I believe. The Soyuz 18A abort occurred late in the ascent, by which time the escape tower would have been jettisoned.
But the fact that an escape tower has saved a crew does not mean it does not carry its own risks. If, for example, there is a 1% of needing a tower to escape a failing launch vehicle (roughly the demonstrated rate over the life of Soyuz) and a 0.1% that the tower itself will kill the crew, then the tower clearly increases safety. If the likelihood of needing the tower is 0.1%, as one might reasonably hope for newer launch vehicles, then it provides no net gain in safety.
Correct about the use of the Soyuz launch escape system. At the time of the manned Soyuz 18-1 abort in 1975 it had already been discarded. It was used for the Soyuz-T 10-1 off-the-pad abort in September 1983 with two cosmonauts on board.
For the latter mission the two men experienced up to 18-20g. Cosmonaut Anatoli Artsebarski said at a meeting of the British Interplanetary Society in 2015 that during training the cosmonauts are only trained up to about 8-9g, so cosmonauts don't get a single "abort profile" experience unless it actually happens.
Remember also that during the L-1 and L-3 programmes unmanned Soyuz-class descent modules were rescued successfully from exploding Proton-K and N-1 launch vehicles using their launch escape systems.
As for "Orion's Weight", the title of this thread, in orbit of course it's zero.
As for "Orion's Weight", the title of this thread, in orbit of course it's zero.
Ahh, technically correct, the best kind of correct !
Mass vs weight; yes, all true. But the weight is certainly relevant when discussing what launcher classes can get Orion off the ground and also; the amount of stress the weight will cause for it's recovery systems. Particularly the parachutes.