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[The Following is an excerpt from
a letter to Allen Meece]
[Updated 14 September 2002]
The following is a rough breakdown
of the estimated mass for the crew cabin, airlock, and externally
attached equipment, made using my plastic hab floorplan. The weights
are based on volume-density calculations or guesses using common
equivalents as a reference (equivalents which may or not be suitable
to the task). Everything is to be considered “off the cuff” baring
further elaboration.
CREW CABIN:
Inner
Pressure Wall (1.25”-walled 3.5x6.5m PET tank) |
2800kg |
Outer
Pressure Wall (Double Dacron-Polypro ballute) |
320kg |
Insulation (R30 Fiberglass,
R15 Styrofoam) |
180kg |
Hab
Frame (2.5mm-walled Al square-beams) |
420kg |
Outer
Load Envelope (Dacron) |
100kg |
Hab
Floor (1.6mm Al sheet) |
80kg |
Bath
Wall (Polypro-Styrofoam) |
30kg |
Hab
Lockers, Shelves, & Cabinets (PET & Aluminum Mesh) |
200kg |
Pressure
Doors & Windows (20mm Pyrex & 5mm+ Al Plate) |
80kg |
Ventilation
System (Polypro Ducts, Dehumidifier, etc.) |
40kg |
Water/Antifreeze
(120gal PET Tanks, H2O, Automotive Ethylene Glycol) |
900kg |
Water
Piping & Dispensers (Sinks, Heaters, Pumps, etc.) |
50kg |
Sewage
System (Latrine, Sink Filter, Boiler, etc.) |
30kg |
H2/O2
Regulation System (Al Tanks, Regulators, Compressors, etc.) |
200kg |
Emergency
Batteries (5kWh Ni-MH) |
40kg |
Emergency
Oxygen Supply (Solid Oxidizer Pyro-Canisters) |
150kg |
Reversible
Fuel Cells (10kW Reversible) |
400kg |
Crew
Cabin Furnishings (Bunks, Chairs, DVD, etc.) |
130kg |
Pilot's
Station (Chair, Console, etc.) |
50kg |
Galley
Equipment (Fridge, Oven, etc.) |
30kg |
Workroom
Equipment (Tools, Laptops, etc.) |
150kg |
Installed
Instrumentation (Experiment Packages, Monitors, etc.) |
400kg |
Crew
& Passengers (5 People) |
500kg |
Crew
Luggage (Fitted Pressure Suits, Clothes, etc.) |
250kg |
Basic
Life Support Supplies (Food, Water, Air for 50 man-days) |
300kg |
Misc.
Life Support Supplies (Cleaners, TP, etc.) |
20kg |
10%
Margin |
700kg |
Crew
Cabin Total |
8600kg |
The crew cabin mass estimate can
be further reduced by using a thinner inner pressure wall, which
will require a custom cast tank. Note that the outer pressure wall
must be reinforced accordingly, but it takes far less mass for
the same load because it isn't subjected to the same stresses as
the inner wall. Mass savings could be as high as 1800kg.
Using Ni-MH batteries for power
instead of fuel cells reduces the Crew Cabin's H2/O2 regulation
system to just 50kg by eliminating the need to crack water for
air, though the batteries will weigh as much as the eliminated
fuel cells. Half the water/antifreeze supply goes away. Also, emergency
batteries become unnecessary, as does most of the emergency oxygen
(because oxygen is delivered in an immediately usable form that
requires little energy or waiting for preparation). Mass savings
could be as high as 800kg for the crew cabin alone, not counting
reductions in the solar array and other platform systems.
Accumulating less dramatic savings
in other systems, the Crew Cabin total mass could be reduced below
5000kg.
AIRLOCK:
Inner
Pressure Wall (1.25” 2.5x2.5m PET Tank) |
900kg |
Outer
Pressure Wall (Double Dacron-Polypro) |
100kg |
Insulation
(R30 Fiberglass, R15 Styrofoam) |
40kg |
Airlock
Frame & Flooring (2.5mm-walled Al square-beam, 1.6mm Al Sheet) |
100kg |
Outer
Load Envelope (Dacron) |
30kg |
Lockers
& Cabinets (Al Mesh) |
50kg |
Pressure
Door & Window (20mm Pyrex & 5mm+ Al Plate) |
40kg |
Air
Regulation & Ventilation System (Tankage, Compressors, Etc.) |
40kg |
Life
Support Supplies (Food, Filters, Water, etc.) |
20kg |
Installed
Instrumentation |
60kg |
Tools
& Equipment |
100kg |
10%
Margin |
150kg |
Airlock
Total Mass |
1700kg |
As with the Crew Cabin, the airlock
mass could probably be pared down by judicious changes. However,
it's simple design (an insulated tank with air cylinders and valves
in it, with a compressor on top) limits these reductions. It will
probably weigh at least 1000kg.
MISC. HAB STRUCTURE:
The Crew Cabin and Airlock are
just two parts of the suspended deck design. Here is the rest:
Suspended
Deck Frame (2.5mm-walled Al Square-beam) |
350kg |
Suspended
Deck Flooring (Al Mesh) |
300kg |
Recovery
Chutes (X-Large chutes, reserve chutes, and 600mph pro-rated drogues) |
120kg |
Cooling
Panels (Polypro Panels & piping) |
20kg |
External
Tankage (Al tanks, boiler, etc.) |
100kg |
Elevator
Dock (Locks, winch, etc.) |
100kg |
Cart
& Tools |
20kg |
Guy
Lines & Netting (1/4”, 1/2” & 3/4” Spectra, w. Tackle) |
100kg |
External
Equipment Mounts & Lockers (Al Sheet & Mesh) |
50kg |
Externally
Installed Instrumentation |
400kg |
H2
Reserve (Liquid H2 & Tankage) |
150kg |
Margin |
170kg |
Misc.
Total Mass |
1900kg |
Using a suspended hab instead of
building it into or over the keel allows a unique emergency evacuation
system: parachuting the entire hab down. My friend Floyd Moore,
a former race car driver and pit crew mechanic, informs me that
the drogues used on dragsters are rated for 600+mph and I think
four or five should be sufficient to keep a 7 ton hab below 300mph
and upright during its descent. Unlike the main chutes, they can
be deployed almost immediately, as they will survive a fall through
the stratosphere so long as they are able to prevent the Hab from
exceeding the speed of sound. Thus, a recovery system is included
in this mass estimate.
Composites are unsuitable for the
flooring, but might replace aluminum in the deck frame. (They may
also be employed in the crew cabin and airlock, which would decrease
their mass still further.)
From this estimate, we can expect
the total hab mass to be between 7700kg and 11000kg. The best way
to get this mass below 7000kg is to use a smaller crew cabin. A
3.5m diameter cabin could be as short as 5m and still sleep 6,
but there wouldn't be room in the cabin for them to do much except
sleep. Eliminating a separate bath partition allows some further
mass reduction. (Reducing the workroom size isn't a viable option
because that's where people are going to be spending their time
with a smaller crew cabin.) Further reductions in crew cabin mass
can be had by limiting the instrumentation aboard, since that determines
power system and other requirements.
That's my first guess as to the
hab mass.
CME
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