Question Deepstar 2.0 Mass

[Mafuskas]

http://orbithangar.com/searchid.php?ID=3251

It's no secret that the Deepstar 2.0 is my favorite interplanetary exploration vessel; but I've recently come across a question of a correct mass for this ship.

In its .ini file, the Deepstar 2.0 claims to have an empty mass of 20000 kg and a fuel mass of 300000 kg. Is this a realistic mass for a spacecraft of this size? (348.5 m)

I am hoping that others on this forum might help me determine some good numbers for this craft or at least help me to find out these figures for myself.


I would like to just message the author himself, but I do not know how active he is with Orbiter at the moment and figured that this way would be more expedient, as well as having the product available for anyone else that might be interested.

Thanks.

 

[Sky Captain]

The correct mass probably would be several thousand tons when empty. By roughly guessing volume of those fuel tanks (~30 m diameter ~100m length I estimated they should contain ~20000 tons of hydrogen propellant. Crew living area of such long duration deep space vessel would need serious radiation shielding which is very heavy. Then count drive system, crew supplies, spare parts, mission related hardware and structural frame to hold all that together. I guess realistic empty mass could be around 2000 - 4000 tons.

 

[Dig Gil]

To determine this I use a simple formula that works with cubes, so it might be inaccurate.
If you want this equation to be more accurate you'll need to cut the ship to pieces of the different sizes and materials it has and apply the formula on each piece.

Density(or Volumetric Mass; not sure what english people call it)= Mass (grams)/Volume (cubic meters)

So,

Mass (grams)=Density (gr/m^3)*Volume (cubic meters)

I think that's correct, but if someone more experienced notices any flaw please tell and write a better formula (if any).

The table below has got some values for the density of materials commonly used in spacecraft (taken from Hyperphysics):

Aluminum 2.7

Copper 8.3-9.0

Iron 7.8

Hydrogen 0.00009

Helium 0.000178

Nitrogen 0.001251

Search for others if needed.

 

[mjanicki]

If I recall correctly, when Deepstar 2.0 was released there was discussion in the old forums about changing the vessel configuration. Some folks who know more about such things than I do seemed to have come up with an alternate config, including much greater vessel mass, that seemed to work well. They included modified configs for the landers as well. It might be worth a look.

The original thread: http://www.orbitersim.com/forum/default.aspx?g=posts&t=19023

-- Mike

 

[eveningsky339]

I could be wrong, but I believe the forward section of the ship (bridge, living quarters) is inflatable, hence the unusually light weight. It certainly has that appearance. But perhaps I am mistaken?

 

[Sky Captain]

I could be wrong, but I believe the forward section of the ship (bridge, living quarters) is inflatable, hence the unusually light weight. It certainly has that appearance. But perhaps I am mistaken?

Radiation would be a problem. For long duration missions out of Earth protective magnetic field crew living area would need thick walls for radiation shielding which translate into lot`s of mass.

 

[atuhalpa]

Hmm. What would be the energy requirements to produce a local magnetic field that would negate the radiation exposure?

 

[Sky Captain]

I just imported Deepstar mesh into mesh wizard and find out fuel tank is 100 m long and 22.2 m diameter so it turns out each tank has a volume of 38700 cubic meters and 193500 cubic meters total volume which would hold 13500 tons of H2.

 

[Tommy]

Actually, radiation shielding for future ships probably won't be as heavy as you'ld think. NASA is currently looking at lightweight plastics with high hydrogen content. Hydrogen is actually one of the best elements for cosmic and solar radiation shielding. An inch or so of a lightweight plastic around crew quarters and bridge, less in areas not usually occupied, would likely add less than a ton to the overall weight. Couple this with lightweight composites, I'd say the vast majority of the mass will be in fuel, engines, and life support (counting food and water).

 

[Mafuskas]

Great discussion everyone, I appreciate all the input.

Ok i calculated the weight and fuel masses for the ship, in relation to space shuttle and its components. A single fuel tank of deepstar is 16,6 times bigger and about 7 times heavier than a space shuttle ET. So we get 16,6 x 720mT (fuel: Hydrogen and oxygen) = about 12000mT fuel. But if deepstar uses only hydrogen, typical for a fusion drive, we can divide by 5, because only 20% in shuttle tank are hydrogen mass. But Deepstar has 5 tanks of it, so we have to multiplide again by 5 . The new shuttle ET are only 26,5mT, we get 26,5mT x 7 = 185,5 mT for a single tank x 5 = 927,5 mT for all tanks empty mass. For the rest of the ship i calculated a mass of 1500 mT, but in 2070 we have better materials, so it should be posible to reduce it to 1000mT. Complet empty mass with tanks then about 2000mT, and thats very good for that monster. For that big mass we can only use a progressively fusion drive. DeltaV is then 193 km/s (before 200).
OK here the new datas, change it in config.ini, because i dont know other way to send it

EMPTY_MASS=2000000
FUEL_MASS=12000000
MAIN_THRUST=40000000
ATTITUDE_THRUST=30625000
ISP=100000

Next step i will reconfig the landers, a nuclear thermal rocket will be more then enough for a single descent and ascent at a airless world

@Ijuin
The Landers have delta-V of about 8 km/s now, before it was 5,6 km/s. I used NASA dates for their new altair moon lander, planed for constellation program. Because the Deepstar lander looks like it. I changed tank propellant from H2/LOX with chemical propulsion to pure H2 with nuclear thermal propulsion. Original NASA lander has a delta-V of only 2,2 km/s :-(

here the new Datas to change for the lander in spacecraft/deepstar-lander-1.ini and ...2.ini

EMPTY_MASS=19000
FUEL_MASS=30000
MAIN_THRUST=0
RETRO_THRUST=0
HOVER_THRUST=200000
ATTITUDE_THRUST=4450
ISP=8800


Here the Datas of project NERVA 2 of NASA
;*Diameter: 10,55 m
;*Lenght: 43,69 m
;*empty mass: 34.019 kg
;*full mass: 178.321 kg
;*thrust at vac: 867 kN
;*specific Impulse (I_{sp}) in vac: 825 s (8.09 kN·s/kg)
;*I_{sp} sea level: 380 s (3.73 kN·s/kg)
;*Burntime: 1.200 s
;*fuel: reactor/LH2
;*nozzles: 1 Nerva-2

I really like the numbers in this post, and plan to try them out as soon as I get a chance. What do you all think of them? Thanks mjanicki for the link!

 

[eveningsky339]

Actually, radiation shielding for future ships probably won't be as heavy as you'ld think. NASA is currently looking at lightweight plastics with high hydrogen content. Hydrogen is actually one of the best elements for cosmic and solar radiation shielding. An inch or so of a lightweight plastic around crew quarters and bridge, less in areas not usually occupied, would likely add less than a ton to the overall weight. Couple this with lightweight composites, I'd say the vast majority of the mass will be in fuel, engines, and life support (counting food and water).

The fuel tanks constitute a major part (about half?) of the Deepstar's length and are at least as wide as the forward crew habitat; fuel alone would be astronomical in terms of mass.

 

[Hartmann]

A good shield could be plastics and water tanks, combined with a magnetic field

 

[MJR]

A good shield could be plastics and water tanks, combined with a magnetic field

I noticed your flag was Antartica. Do you really live there?

 

[Dig Gil]

I noticed your flag was Antartica. Do you really live there?

I didn't knew there was such banner. fftopic:

 

[Brycesv1]

lol hows the internet down there?

back on topic. exactly how do the changed config numbers affect ship performance? more DeltaV over more time or vise versa? something completely different?

 

[jedidia]

I use the deepstar currently with a mass of 1000 tons, fuel mass 400 tons, and a fusion engine with an Isp of 1000000 (allthough, that's really Ve, but it seems that Spacecraft3 takes Ve as Isp) and 50000 newtons of thrust, for experimenting around with low-thrust long-burn flights. The reason for this data is that I have a ship in the make with pretty much these properties, and want to see how it will perform and to figure out best practices for low thrust trajectories with current nav-tools. The DeepStar is still a little bit bigger than the ship I'm designing, and even there I reduced mass a generous amount for reasons of "future advances in light weight materials". The original mass of the deepstar is, if I remember correctly, 200 tons... that's less than my fusion engine alone, so the DeepStar as it is is HEAVILY underweight. (allthough, quite a significant amount of mass of my ship are radiators, and the DeepStar is terribly short of these. I don't really know where it goes with its heat...)

 

[ddom2006]

You couldn't actually guide the Deepstar into any kind of planetfall though right? I don't see any kind of evident heat shield, It probably explains this somewhere and I just missed it :lol:

 

[Sky Captain]

You couldn't actually guide the Deepstar into any kind of planetfall though right? I don't see any kind of evident heat shield, It probably explains this somewhere and I just missed it :lol:

Yep Deepstar is strictly space ship built in space and never meant to touch planetary surface or atmosphere, for that you have those two landers docked.

 

[ddom2006]

Yep Deepstar is strictly space ship built in space and never meant to touch planetary surface or atmosphere, for that you have those two landers docked.

The landers are equipped with heat shields? I thought they were more like the Altair. I started with the Deepstar docked to the ISS the other day and couldn't undock from the ISS because the Deepstar doesn't have reverse retros and therefore I couldn't pull away from the ISS before it redocked. Perhaps I'm just not very good with new spacecraft? :lol:

 

[Sky Captain]

The landers are equipped with heat shields? I thought they were more like the Altair. I started with the Deepstar docked to the ISS the other day and couldn't undock from the ISS because the Deepstar doesn't have reverse retros and therefore I couldn't pull away from the ISS before it redocked. Perhaps I'm just not very good with new spacecraft? :lol:

The original landers are meant to land only on airless planets and moons, but you can always dock a Deltaglider IV or XR2 to Deepstar for atmospheric excursions.

You are right Deepstar don`t have retro thrusters, but you can always use RCS set to translation mode if you have to go in reverse.