[grinich]

Shuttle flew a decent number of missions for the National Reconnaissance Office, conducting secret experiments and deploying spy satellites. Most of the missions are still classified, but many folks have said the military needs drove the design of the Shuttle program. There are pretty obvious advantages to a spaceplane if your goals include capture of enemy satellites. http://www.space.com/34522-secret-shuttle-missions.html

It turns out a lot of science space research is heavily driven by military space presence. For example, Hubble has a 2.4m mirror because there was already a factory making that size for dozens of spy satellite. https://en.wikipedia.org/wiki/KH-11_Kennen

And ever heard of "The Dish" at Stanford? It's a 150-foot radio telescope the US Air Force funded during the Cold War to ostensibly "study the chemical composition of the atmosphere." Total BS. The Air Force built it to intercept signals from Soviet radar systems after they bounced off the moon.

(Thankfully Stanford got to keep it and it's been used for hundreds of projects since then.)

[kabdib]

Regarding Hubble, the intelligence community knew of significant design flaws in Hubble based on their experience with similar hardware, and did not communicate the problems to the Hubble team, for security reasons. This was much more about solar array flex and the Southern Magnetic Anomaly (high radiation zone that is often transited by Hubble, and which tends to crash the processors running the scope); the mirror flaw wasn't known by the TLAs.

The book _The Hubble Wars_, which describes most of this, made me pretty angry that an important scientific instrument was nearly crippled by the "national security" mindset.

[creshal]

Retrieval of objects in space and bringing them back to Earth is about the only mission where the Space Shuttle was superior to capsule designs. This was also used in a handful of science missions for studying long-term exposure of various materials.

But the vast majority of the Shuttle's 130 flights would have been better served by an Apollo or Gemini derived design.

[grinich]

From what I've read, Shuttle also did quite a bit of satellite repair (like fixing Hubble). And the orbiter's cargo bay certainly was useful to transport many parts of the ISS.

The Department of Defense still actively uses a spaceplane-ish vehicle. It's just a much smaller unmanned one called the X-37b. Many folks speculate it's used to repair and refuel spy satellites, and potentially even rendezvous with and and hack enemy satellites. https://en.wikipedia.org/wiki/Boeing_X-37

Generally I totally agree though-- capsule design makes way more sense for anything leaving or reentering atmosphere. The upcoming Orion are clearly in that directly.

[creshal]

> From what I've read, Shuttle also did quite a bit of satellite repair (like fixing Hubble)

It did, but a capsule can do the job just fine too – for JWST, it is (or was) planned to do repairs using the Orion capsule and a mission module docked to it.

> And the orbiter's cargo bay certainly was useful to transport many parts of the ISS.

Kinda, yes. But an unmanned rocket could have done the same job, and likely cheaper than the Shuttle.

Most of the civilian Shuttle missions could have been easily served by other, much cheaper craft – but who knows what happened during the classified ones, it might actually have been cheaper to the taxpayer at large (if not NASA) to have one craft to serve both roles.

> The Department of Defense still actively uses a spaceplane-ish vehicle. It's just a much smaller unmanned one called the X-37b. Many folks speculate it's used to repair and refuel spy satellites, and potentially even rendezvous with and and hack enemy satellites. https://en.wikipedia.org/wiki/Boeing_X-37

We don't really know, but given how little fuel capacity it has and how long it stays in orbit, it's more likely that the DoD's stated purpose of long-endurance testing of new spy hardware is true.

[grinich]

I'm pretty sure we're not going to send any capsule to repair the JWSP. It's going to be at L2 which is 1 million miles away from Earth, or about 3x furthest than mankind has ever traveled. It would take weeks to get there.

[dotancohen]

The X-37 has demonstrated over ten times the delta V of the space shuttle. Why do you assert that it a limited fuel capacity?

[LeifCarrotson]

If the rumor is that it's being used to refuel satellites, there are two considerations:

1. Can it get to many satellites? Yes, it has good delta V, though I think you're mixing the X-37's delta V with its boosters and the delta V of the Shuttle orbiter without its SRBs and external tank.

2. Can it carry fuel for those satellites? No, not much. The X-37 has a maximum total takeoff weight of 5000 kg, while the Shuttle can get 27000 kg to LEO. Unfortunately, only one X-37 will fit in the payload bay of the Shuttle, so we can't actually lift five X-37s in the Shuttle.

Many large satellites weigh more than the X-37's total mass. The biggest individual consumer, the ISS, requires about 7000 kg of fuel annually to stay in orbit. A KC-135 in-air refueling tanker is much faster than an oceangoing supertanker, but you wouldn't use the former to empty an oil rig!

[grinich]

The ISS needs that much fuel to boost it's altitude due to drag in LEO. But the refueling of satellites by the X-37 is hypothesized to be at much higher altitudes where there is very little drag.

These satellites don't need altitude boosts-- they use propellant for orbital changes (e.g. to "re-task" a spy satellite to a new region). But instead of chemical rockets they often use xenon gas ion engines.

The key thing with ion drives is their "specific impulse." High-thrust chemical rockets are needed to get out of the atmosphere and perform fast burns, but ion engines are often >10x more efficient once already in orbit. And because there isn't a chemical reaction, there is less corrosion and they can last for years.

Refueling xenon for the ion drives of spy satellites would double or triple their mission lifespan. They don't need much -- maybe just a couple hundred kg. And this could literally save billions of dollars since these satellites are so expensive to build.

https://en.wikipedia.org/wiki/Specific_impulse#Examples

[creshal]

Where have you gotten that from? The only numbers I can find for observed Δv changes are some 100m/s for USA-212, which is a third of the OMS' rated 300m/s with a full cargo bay.

[dotancohen]

For one thing, the X-37 Wikipedia page states that a design goal was 3.1 KM/s Delta-V. That's about as official a number as I'm finding online (blah blah Wikipedia source), but there are quite a few people who track these things in the sky. Each orbital inclination or altitude change requires a minimum delta V to execute, and we can observe the results of these maneuvers here on Earth. Online arguments about the X-37 delta-V are inconclusive, we'll leave it at that!

[dotancohen]

The shuttle was also great for anything that required an EVA, and could handle multiple EVAs on a single mission. It could also stay in orbit with a large crew for extended periods.

Those old boats had capabilities that I don't think we'll see for another two generations of manned spacecraft.

[creshal]

> The shuttle was also great for anything that required an EVA, and could handle multiple EVAs on a single mission.

Gemini, Vokshod, Apollo and Soyuz all demonstrated that ability as well. Apollo especially with multiple lunar EVAs per mission.

The Shuttle's biggest advantage over all those was being roomier, making EVA preparations less of a hassle, but all space craft currently in development are addressing that shortcoming.

> It could also stay in orbit with a large crew for extended periods.

Meh. Yes, it could… but should it? In that role, the Shuttle was still inferior to a real space station, while being as expensive. If it wasn't for political reasons (Shuttle was approved, but it was hard to fund anything else), NASA likely would have preferred using a space station for it (and largely did, once it could access Mir/ISS).

ISS isn't going away for a while yet, the industry is working on smaller private space stations that could be rented out for this purposes, and NASA is contemplating building smaller stations in deep space when/if necessary. We didn't actually lose any capability.

[dotancohen]

Important to note that the Shuttle did not require cabin depressurization to EVA, it had an airlock. None of those other vehicles could keep the cabin pressurized during an EVA (I'm not sure about Soyuz, for that matter).

[peteboyd]

Keep in mind it was NOT an all or nothing proposition for using the Shuttle. We launched satellites while the shuttle was running using Titan, Atlas, and Delta rockets. I would imagine if it was more cost efficient to use those rockets, they would have done so.

https://en.wikipedia.org/wiki/List_of_Titan_launches and https://en.wikipedia.org/wiki/Delta_IV and https://en.wikipedia.org/wiki/Atlas_V

[maxerickson]

There's a difference between the shuttle being used for certain missions and the shuttle being necessary for those missions.

(and then going up a level, whether those missions were necessary to establish those capabilities or if different missions would have been used in the absence of the shuttle)