Question General Spaceflight Q&A

statickid

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On one of the two service structures, that are rotated into the horizontal before launch.

>IMG

AFAIR, it is the left one in the photograph that contains the elevator.

>IMG

Here you can see it better, the blue cabin left of the left worker.
it's a surprisingly "small" rocket with the people in view there. It really goes to show how bulky the space shuttle was lugging all that wing and hull up.
 

Urwumpe

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it's a surprisingly "small" rocket with the people in view there. It really goes to show how bulky the space shuttle was lugging all that wing and hull up.
More lugging also 20 tons of payload and 4 more astronauts up.
 

orbitingpluto

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I'm currently playing with a few ideas for building a space station with the Space Shuttle, and I'm wondering about OMS assists. I know the explanation is that they add extra thrust and lower the Shuttle's mass on high inclination, high orbital altitude missions, but I'm unclear on how to use OMS assist in Orbiter. Is there a formula or a rule of thumb that I can plug the intended inclination and altitude of the station, plus payload into and get the duration and start time of my OMS assist? I'm using Shuttle Fleet, so these are the parameters I can work with(copied out of the Shuttle Fleet manual):

ASSIST <xxx> <yyy>

During Direct Insertion launches; this will cause an
OMS assist.
<xxx> is the OMS assist start time in seconds MET.
It only works for times from 130 to 200, anything else
will default it to 135 seconds.
<yyy> is the OMS assist burn length in seconds.
It only works for durations from 0 to 135, anything
else will default it to 77 seconds.
If <xxx> and <yyy> are omitted the autopilot defaults
to 135 seconds for start and 77 seconds duration.
Knowing what real life missions did going to the ISS is useful, but since I'm free to put my station at 45 degrees relative to the equator, or 30, or 60, or 28, or even in a polar orbit out of Vandenberg, knowing the deeper whys and hows seems like a better route than guessing and testing. Especially since I don't have great gobs of time to do the testing.
 

orbitingpluto

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I wish there is a recent Shuttle mission planner's guide out there I could poke around in, but if there is I haven't found it yet. I did make some progress on answering my own question about OMS assists. For payloads to various inclinations and altitudes, I'm quoting the following from the Shuttle news reference guide. It's from 1988, but also what I have so far. I've added the metric equivalents beside the original English measurements for easier understanding.


NASA's latest assessment of orbiter ascent and landing weights incorporates currently approved modifications to all vehicle elements, including crew escape provisions, and assumes a maximum Space Shuttle main engine throttle setting of 104 percent. It is noted that the resumption of Space Shuttle flights initially requires more conservative flight design criteria and additional instrumentation, which reduces the following basic capabilities by approximately 1,600 pounds(725.74 kg):

¥Kennedy Space Center.Eastern Space and Missile Center (ESMC) satellite deploy missions. The basic cargo-lift capability for a due east (28.5 degrees) launch is 55,000 pounds(24,947.58 kg) to a 110-nautical-mile (126-statute-mile)(203.72 km) orbit using OV-103 (Discovery) or OV-104 (Atlantis) to support a 4-day satellite deploy mission. This capability will be reduced approximately 100 pounds(45.35 kg) for each additional nautical mile of altitude desired by the customer.


The payload capability for the same satellite deploy mission with a 57-degree inclination is 41,000 pounds(18,597.28 kg).


The performance for intermediate inclinations can be estimated by allowing 500 pounds(266.79 kg) per degree of plane change between 28.5 and 57 degrees.

If OV-102 (Columbia) is used, the cargo-lift weight capability must be decreased by approximately 8,400 pounds(3,810.17 kg). This weight difference is attributed to an approximately 7,150-pound(3,243.18 kg) difference in inert weight, 850 pounds(385.55 kg) of orbiter experiments, 300 pounds(136.07) of additional thermal protection system and 100 pounds(45.35 kg) to accommodate a fifth cryogenic liquid oxygen and liquid hydrogen tank set for the power reactant storage and distribution system.


¥Vandenberg Air Force Base Western Space and Missile Center (WSMC) satellite deploy missions. Using OV-103 (Discovery) or OV-104 (Atlantis), the cargo-lift weight capability is 29,600 pounds(13,426.33) for a 98-degree launch inclination and 110-nautical-mile (126-statute-mile)(203.72 km) polar orbit. Again, an increase in altitude costs approximately 100 pounds(45.35 kg) per nautical mile(1.85 km). NASA assumes also that the advanced solid rocket motor will replace the filament-wound solid rocket motor case previously used for western test range assessments. The same mission at 68 degrees inclination (minimum western test range inclination based on range safety limitations) is 49,600 pounds(22,498.18 kg). Performance for intermediate inclinations can be estimated by allowing 660 pounds(299.37 kg) for each degree of plane change between inclinations of 68 and 98 degrees.
I also found a rule of thumb in a Shuttle O&A thread on the nasaspacleflight forums here, with the relevant section below. Again, I've added metric equivalents.

OMS assist is performed if 1) the OMS prop required for the mission itself does not require full tanks and 2) the mission could benefit from the additional payload capacity gained by filling the OMS tanks full and burning the difference as OMS assist (IIRC it's roughly 200 lb(90.17 kg) payload for 4000 lb(1,814.36) OMS prop).
And to get a handle on just how much propellent the OMS tanks have, I grabbed this info off [ame="http://en.wikipedia.org/wiki/Space_Shuttle_Orbital_Maneuvering_System"]Wikipedia's OMS page[/ame]:

When full, the pods together carried around 8,174 kilograms (18,021 lb) of MMH and 13,486 kilograms (29,732 lb) of N2O4, allowing the OMS to produce a total of around 1,000 feet per second (300 m/s) of delta-v.[4][5]
Doing a bit of addition, I get 21,660 kg of propellent, but in order to figure out what propellent I can expend during ascent(and thus how much extra payload an OMS assist will gain me), I'll need to know how much propellent is needed for maneuvers during a particular mission, like for rendezvous and especially reentry. That's a different question than the one I asked though, and for the moment I'm content to leave that for another day.
 

sorindafabico

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I don't want to open a thread for this, so I'm asking here...

Is there any reason for Hellas Planitia being still unexplored by rovers? Being the lowest place on Mars, it's atmospheric pressure is greater than the triple point. Maybe its distance from the equator is a no-go for liquid water (lower temperatures), but...Any other reasons or it's just waiting its time for being explored?
 

statickid

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I'm going to post this here, just for anybody searching the archives:

Question: How big is the solar system? Are there any good visualizations of this?

Answer: I just found this website, it is awesome and a great demonstration:

pixelspace

Check it out!! maybe this should be called "orbiter mobile"
 

Unstung

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I have a couple questions regarding the Dragon V2 reveal yesterday involving how SpaceX wants to have a lot of reusability.

1. Will the parachutes on Dragon have to be examined after every successful landing, even if not used? It seems pointless to not use the parachutes yet have to check and possibly repack them after every flight to ensure their condition for crew safety.

2. Is a reusable heat shield that can just fly again without any repairs or little examination (like the parachutes) possible? It also seems very risky. The shuttle tiles had to be repaired and/or reattached (or even replaced) after every flight, IIRC.
 

PhantomCruiser

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I don't think the chutes themselves would have to be repacked if not used. But then I don't know I'm just guessing. The pyrotechnics might be another story.

A 'rigger would be able to answer better.

The heat shield is an ablative type, just like Apollo. Have to see the data to see how much material remains after a flight, and see how much thickness is required for a return from LEO (and add in a comfortable margin for error and that demon Dr. Murphy).
 

soumya-8974

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Some questions regarding Falcon 9:
  • How the Block 5 iteration of Falcon 9 is 100% reliable given the boosters are not refurbished after landing?
  • How SpaceX is able to land the Falcon Heavy boosters simultaniously?
 

Urwumpe

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Some questions regarding Falcon 9:
  • How the Block 5 iteration of Falcon 9 is 100% reliable given the boosters are not refurbished after landing?
  • How SpaceX is able to land the Falcon Heavy boosters simultaniously?
1. Could be plain luck. Also, little is know how much refurbishment really happens after landing. The structure can likely survive a few thousand tanking cycles before showing too many fine cracks - so all that has to be refurbished is engines, valves or electronics.

2. GPS and autopilot - I am sure, there is no human interaction needed except for range safety. Everything else is just about maintaining enough spacing = returning the boosters on slightly different trajectories to slightly different landing zones.
 
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