Inflatable Martian flyby spaceship

Check out the Vis Viva Equation and the Rocket Equation

Vis Viva gives you the velocity required to carry out a mission

Vf^2 = mu * (2/r - 1/a)

and

The rocket equation (aka Tsiolkovsky equation) is used to calculate
the propellant fraction needed to accelerate a rocket to a desired
velocity knowing its exhaust velocity

Vf = Ve * LN(1/(1-u))

So, what 'seems right' can be calculated with some precision - using a
little knowledge of rocket performance and interplanetary space.

On Dec 6, 4:11*pm, William Mook wrote:
Check out the Vis Viva Equation and the Rocket Equation

Vis Viva gives you the velocity required to carry out a mission

* Vf^2 = mu * (2/r - 1/a)

and

The rocket equation (aka Tsiolkovsky equation) is used to calculate
the propellant fraction needed to accelerate a rocket to a desired
velocity knowing its exhaust velocity

* Vf = Ve * LN(1/(1-u))

So, what 'seems right' can be calculated with some precision - using a
little knowledge of rocket performance and interplanetary space.

An inflatable spaceship seems oriented toward reducing structural mass
by replacing hardshell structure with fabric structure of some sort.
Its best to do a mass budget of the spacecraft you propose to build.

I've done this sort of thing, along with a lot of other interested
aerospace engineers, beginning with vonBraun back in the late 40s, and
I have come up with a series of minimum missions. I even got
published in an Australian newspaper after giving a paper at an AIAA
conference in the 1980s entitled 'Minimum Manned Moon Missions' - this
after NASA said it would take $150 billion to return to the moon after
getting there from scratch for $20 billion in the 1960s! lol. What's
up with that? Bottom line we could go to the moon for less than $1.5
billion - and recently with the development of MEMs based rocketry -
that's reduced to $0.48 billion!!

By far the minimum mass is achieved by using LONG DURATION MECHANICAL
COUNTER PRESSURE SUITS WITH MEMS SKIN - to maintain cleanliness and
health of the wearer as gases and fluids are exchanged. Virtual
reality hardware built into the helmets - along with a 'man
multiplier' used as a haptic device in the long duration suit. In
this way, various environments can be simulated in free space without
any additional hardware at all. The suit itself masses about 20 kg
(44 lbs) - per crew member.

The big mass budget is life support. But with MEMs devices, these too
are made supremely reliable and very lightweight. Consumables for
long-duration missions is the critical issue.

This is addressed by clever use of cryogenic propellants.

http://www.scribd.com/doc/20053585/M...space-Overview

While some have budgeted 22 kg per person per day to maintain a very
lush life style - Gemini and Mercury astronauts consumed 0.77 kg per
per day for non-renewable consumables.

Using a hydrogen/oxygen propellant combination, and using the ullage
and out-gassing of long duration propellants to generate energy with
fuel cells, and then use the water to drink and reconstitute foods,
and then use the waste water to evaporate to control heating (combined
with the fuel cell's heat) - allows us to use less 282 kg per person
per year. So, the mass budget becomes for a 2.5 year mars mission;

500 kg - consumables
200 kg - suit, life support
100 kg - astronaut

800 kg - total

Another 1,100 kg of hydrogen and oxygen consumed over the same period
- taken from the ullage/boil-off of the cryogen propellants carried
along.

2,000 kg per person per mission.

To accelerate from say 7 km/sec to 12 km/sec to travel to Mars,
requires a delta-vee of 5 km/sec. With a 5% structural fraction for
the rocket stage, and an exhaust velocity of 4.5 km/sec - the
propellant needed is;

u = 1 - 1/exp(5.0/4.5) = 0.670807012 ~ 67.1%

propellant fraction

Subtracting 5% and this value from 100% obtains

100.0% - 67.1% - 5.0% = 27.9%

So, for each person we send to Mars, we need to propel

1/0.279 = 3.585 tons

We actually need two stages for this... since we need to project an
object with a speed of about 5 km/sec from the surface of Mars to send
it back to Earth.

So, we square this figure

3.585^2 = 12.847 tons

And 1.1 tons which is only 1/8th the total propellant - can properly
be called Ullage (the gas left over in an empty tank) and boil off.

With an ideal mix ratio of 6 to 1 (not stoichiometric which is 8 to 1
- but more hydrogen rich to reduce molecular weight and improve
performance of exhaust) we have about 2 and a fraction tons of
hydrogen and 10 and a fraction tons of oxygen. Hydrogen is 0.07 tons
per cubic meter and oxygen is 1.14 tons per cubic meter so total
volume is 2/0.07 + 10/1.14 = 37.34 cubic meters - a sphere about 4
meters in diameter.

So, the bulk of this is the empty hydrogen tank from the first stage -
which is about twice the height of a person! Obviously a suited
astronaut would use such an empty shell as housing.

This was the whole idea behind a 'wet' Skylab concept. The booster
rockets could be used as habitats for the journey out.

An SSTO rocket, capable of carrying 4 tons to LEO would also be
capable of being used as a second stage atop a 500 ton first stage -
with the same SSTO capability - to loft a person to Mars and return
them. This is achievable using MEMs rockets.

A fully reusable system - consisting of say a dozen launchers - would
launch a dozen upper stages every synodic period (2.15 years) - and
the hydrogen tank would be sectioned so that an astronaut could enter
the larger empty portion and pressurize it, with oxygen, and take his
or her suit off if needed.

A well crafted long-duration suit would avoid the need for taking the
suit off and take good care of the astronaut inside. In fact, with
MEMs technology one might imagine a suit with propulsive skin
sections Similar to this;

http://www.youtube.com/watch?v=mzXwctPXT4c

With Hydrogen/Oxygen propellant, we'd need tanks. But as a second
stage, to a larger first stage, or the third stage of a slightly
larger two stage to orbit RLV, the astronaut could be in a long-
duration suit, 'lifting' an aerodynamic tank, filled with hydrogen/
oxygen that s/he would ride down to Mars surface, and then 'lift' back
to Earth - and ride to a landing on Earth on their return.