Commercial and US Government Launch Vehicles > Commercial Space Flight General

The Generic Lightweight Manned Spacecraft Thread

<< < (3/18) > >>

cb6785:
Just to have some figures to compare:

Mercury on orbit mass before retro: 1.354 kg

Gemini on orbit mass (Reentry module and retrograde module without equipment module): 2.574 kg

mr.columbus:

--- Quote from: Crispy on 07/22/2008 10:25 am ---I don't think we can require a dedicated docking airlock. It'll have to be APAS. Can we get a mass figure for that? Approx 280kg?

--- End quote ---

APAS is about 250kg.

But, let's disregard the docking mechanism for a second. The Mercury capsule is a good starting point for mass projections, as it was a one-crew low-mass spacecraft:

1. Structure + Heat Shield
Mercury: structure 340 kg, heat shield 272 kg, length 4m; diameter (max): 1.9m; habitable volume: 1.7m
a. The structure was made of nickel-alloy and titanium. Even with lighter materials and an even smaller outer size and habitable volume, I doubt we can shed much more than 100kg from the structure. So for our GLMS, we could assume a minimum of 250kg for structure.
b. Choosing a leightweigh heat shield material such as PICA (density 230kg/m) we can significantly reduce the mass requirement for that part of our GLMS. I would estimate we could at least get down to 150kg (assuming we also reduce the overall outer structure diameter a bid)

2. Navigation, telemetry and communications
Mercury: Navigation equipment 40 kg; telemetry equipment 50 kg; communications systems 20 kg.
Due to modern computer and telecommunication technology we can easily say that we reduce the mass budget allocated to those systems to less than half, or 50kg.

3. Electrical equipment/Batteries/solar cells
Mercury: 80 kg - 13kW batteries (total) for 1.5days maximum
Because we want longer flight durations and even a docking to a space station, our power system will need to be upgraded, preferable with a mix of solar cells and batteries. Requirement for GMLS: 100kg

4. RCS system
Mercury: reaction control system 40 kg; 14kg propellant; 6 x 107 N + fine: 6 x 4.45 N thrusters

While for our purposes we may reduce the number of thrusters and their mass, we will need to increase propellant due to required docking maneuvers. 30kg RCS and 70kg propellant -> 100kg

5. Crew seat, environmental systems, provisions, one person's mass
Mercury: crew seats & provisions 80 kg; crew mass 72 kg; environmental control system 50 kg;

Obviously, we can't assume less than 72kg for the astronaut... while we may reduce the environmental controls mass due to modern technology, we will need to increase provisions for longer than 1.5days in orbit. For our GLMS -> 250kg

6. Reentry/Recovery equipment
Mercury: recovery equipment 60 kg
This includes parachutes, lifewest and boat for a water landing etc. We still need the parachute system, even if we not land on water and possibly even retrorockets for a soft enough landing. Well, let's calculate 50kg.

7. Oribal propulsion system/LAS
Mercury LAS: 580kg escape tower; Escape motor: 231.3 kN, 1 s burn
Separation motor: 3.56 kN, 1.5 s burn; Propellant: solid
Mercury Retro Pack: 3 retrorockets 237 kg; Propellant mass: 205 kg
Retrograde motors: 3 x 4.45 kN, 10 s burn; Propellant: solid

For docking to a space station we would require much more than just some solid motor retro rockets. My suggestion would be to integrate the LAS into the propulsion system of the GLMS. In essence use a number of solid rockets (20+). Fire them together in the event of a launch abort. Otherwise use them for orbital maneuvers. Say 400kg for that system.

However, for smaller orbital burns we will use the RCS system (thus the higher propellant requirement as mentioned above).

Total mass:
Structure 250kg
Heat Shield 150kg
Avionics, flight computers, telecommunication 50kg
Power systems 100kg
RCS system 100kg (thereof 70kg propellant)
Environmental systems, provisions, interior 180kg
One person crew 75kg
Reentry systems/parachute/survival gear 50kg
Main orbital propulsion system (solids) 400kg (thereof 375kg propellant)
----------------
Sum:1335 kg

A docking port (APAS 250kg or CBM 310kg or LIDS ? kg) would add quite some mass to our GMLS (we also need to consider additional propellant + structure for that) -> 1800 kg. Alternative as suggested above: airlock docking.

Mercury specs: http://www.braeunig.us/space/specs/mercury.htm

Jim:

--- Quote from: mr.columbus on 07/22/2008 12:42 pm ---
3. Electrical equipment/Batteries/solar cells
Mercury: 80 kg - 13kW batteries (total) for 1.5days maximum
Because we want longer flight durations and even a docking to a space station, our power system will need to be upgraded, preferable with a mix of solar cells and batteries. Requirement for GMLS: 100kg

4. RCS system
Mercury: reaction control system 40 kg; 14kg propellant; 6 x 107 N + fine: 6 x 4.45 N thrusters

6. Reentry/Recovery equipment
Mercury: recovery equipment 60 kg
........ 50kg.

7.  For docking to a space station we would require much more than just some solid motor retro rockets. My suggestion would be to integrate the LAS into the propulsion system of the GLMS. In essence use a number of solid rockets (20+). Fire them together in the event of a launch abort. Otherwise use them for orbital maneuvers. Say 400kg for that system.


--- End quote ---

3.  Solar panels and associated avionics and mechanisms are going to weigh more than 20 Kg

4.  Going to need more thrusters for translation and coupled rotations.  Also more prop for rendezvous.

6.  How can it be lighter? 

7. Not viable.  Messing with the LAS by adding functions reduces it's reliability and negates its basic task.  Safety devices are not to be used as part of normal operations. 

Also using fixed impulse SRM's are not viable for orbit maneuvering.

kevin-rf:
Another thing to consider with the LAS is mercury did not drag it all the way to orbit.

As far as batteries go, the technology has advanced significantly, anyone have the mass per AmpHour for current batteries? I assume they used Lead Acid during mercury, LiPo's are so much lighter for the same energy storage. Something is wrong with your quoted battery storage, it should either be Amp Hour with a voltage or KWatt Hour. I think it would be fair to assume you want as a min the same Amp Hour storage as Mercury.

Mr. Columbus, thanks for the breakdown, it gives people something to argue with instead of the traditional arm waving of modern materials will make it X-Factor lighter.

gospacex:

--- Quote from: mr.columbus on 07/22/2008 07:51 am ---you need to think about alternative docking mechanisms. For instance a CBM unit clocks in at 310kg (200kg the mechanism and 110 kg the hatch) - APAS is smaller and a bit lighter.
--- End quote ---

I say let the astronaut don the EVA suit and ride in it entire way to orbit. When you are at ISS, you can enter it through existing EVA entrance(s). Capsule does not need to have a ISS compatible docking mechanism, one which allows astronaut to leave the capsule for EVA is enough. Heck, for especially adventurous astronauts capsule can be even not pressurized at all! :) :)

Pros:
* EVA suit would save the astronaut from dying from depressurization (for example, Challenger astronauts become unconscious seconds after Orbiter breakup).
* If previously EVA suits were part of the cargo, now they are a useful part of life support.
* EVA suit is required anyway if some abort scenarios require ejection at high altitude.

Cons:
* EVA suit is bulky to wear.


--- Quote ---Also, in order to use your vehicle as a lifeboat and have it stay long-term (6months+) at the station, you need micrometeroid/radiation shielding and thermal systems, which will also be more than 100kg at least.
--- End quote ---

Ditch this requirement. Have separate (heavier) capsule design for this purpose.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

Go to full version