Dan's Orbiter page
Orbiter English => Dan's add-ons => Topic started by: acehunter on 04 February 2004, 22:38:17
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For those who are interested, and for Dan if he chooses to include thermal effects in the DGIII:
The DGIII appears to have a total sustained electrical output of about 8-9kW (Based on the
maximum ~85Amps I was able to draw with all systems powered and opening all doors
simultaneously).
The STS fleet generates 14kW sustained and 24kW maximum. The shuttle radiators radiate
100,000 BTU and have a combined surface area of 1600 square feet. (148 m2) An equivalent
radiator on the DGIII would be approximately 900 square feet. (85 m2) The existing radiator on
the DGIII looks to be about 100 square feet. (9.3 m2) Either the radiator on the DGIII is *really*
efficient, or the craft radiates heat through parts of the hull in addition to the radiator.
Heat is the primary problem and enemy for any spacecraft. The STS fleet sheds heat through a
freon cooling system, which is routed through the radiator panels when the cargo bay doors are
open. During ascent and landing, the system routes the freon through flash evaporators
containing water. Water takes an enormous amount of energy to bring from cold temperatures to
the boiling point, and these evaporators serve as a temporary heat sink until the payload bay
doors can be opened and the radiators deployed. The waste heat from the freon system is also
used to warm cryogenic O2 to "room temperature" before it is pumped into the main cabin. Apollo
generated power comparative to the STS, and had small radiators in the skin of the CSM.
Additional heat was shed through the service module walls. Shedding heat is more of a problem
for the STS and the DGIII because of the thermal protection system for re-entry. thermal tiles and
RCC panels make the shuttle into a giant thermos, requiring it to radiate nearly *all* of its heat
through the radiators. Capsules had ablative heat shields that burned away, and had good heat
conductivity compared to today's spacecraft. A lot more heat was radiated from the skin, so the
radiators could be smaller.
Without enough radiator surface, a spacecraft will heat up in the cabin and internal electronics,
eventually causing systems to fail. The issues become somewhat lessened as distance from the
sun increases, or by changing the ship's albedo. (reflectivity) This, of course, is why the ISS and
the shuttle are white.
Corrections, comments, etc welcome. Apologies if this was too dumbed-down or too technical for
certain people - trying to explain in plain terms for those who want to know. Personally, I hope
Martin puts some kind of heat model into Orbiter in the future. (or is there one? Still going
through the API manual in the SDK)