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I have long believed that Enterprise was just an empty craft, with only the instruments to operate in shorts flights in the atmosphere.
Basically a large glider with odd wings.

However, I have been seeing Enterprise referred to as not space-rated or space-ready, and sometimes as an 'orbiter'. (For example Space Shuttle Orbiter Approach and Landing Test: Final Evaluation Report that is linked in @OrganicMarble's answer calls it "Orbiter 101" a few times)

This makes it seem like Enterprise was actually a complete Space Shuttle, but missing some testing or without a few required space elements.

How much of a prototype actually was Enterprise?

It apparently did not have engines, but the other shuttles also needed to refurbish the engines after each flight.

Speedphoenix
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    I think I've been guilty of referring to Enterprise as an orbiter when talking about the shuttles as a fleet; it's a bit awkward to say "STS orbiters-and-gliders". I don't think I realized before now how appropriate it was that the "pretend spaceship" was named after a "pretend spaceship!" (--and I say this as a lover of Star Trek). – Russell Borogove Jul 17 '20 at 18:27
  • @RussellBorogove This is where I saw Enterprise being called an orbiter https://www.quora.com/Why-wasnt-the-space-shuttle-Enterprise-ever-sent-into-space – Speedphoenix Jul 17 '20 at 21:35

1 Answers1

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Your belief was pretty correct.

Major systems missing on Enterprise:

  • orbital manuvering system
  • reaction control system
  • main propulsion system
  • space radiators
  • airlock
  • star trackers
  • thermal protection system (tiles)
  • cryogenic tankage for fuel cell reactants
  • payload bay payload mounting hardware
  • galley
  • aft and overhead windows
  • Ku-band antenna

Major systems different on Enterprise:

  • hydraulics
  • electrical
  • thermal control
  • cockpit controls and displays
  • structure
  • communications

Enterprise-only systems

  • nose-mounted air data probe
  • high pressure tankage for fuel cell reactants
  • flight test instrumentation
  • umbilical to 747 mothership
  • tracking beacons
  • ram air scoop

She was intended only for testing the final stages of aeroflight1 so had only systems required for that installed.

1 The original plan was to convert her into a spaceworthy orbiter by adding the missing systems but it ended up being too expensive, largely because of structural design changes to the wings, mid-fuselage, and thrust structure. Challenger was built out of the structural test article instead.

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References

Organic Marble
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  • Are those lead ballasts in the first figure present in the space rated orbiters too or are they to simulate the weight of missing components? – Speedphoenix Jul 17 '20 at 12:05
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    Definitely the latter, but the operational Orbiters had ballast too: https://space.stackexchange.com/a/43749/6944 Enterprise almost certainly had extra. – Organic Marble Jul 17 '20 at 12:08
  • Did Enterprise have good life support? Or things like crew beds and a toilet? – Speedphoenix Jul 17 '20 at 12:35
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    @Speedphoenix I looked for details on the life support system but none of the references really mentioned it :( That "ram air" thing probably took the place of some of it. I would guess you are correct on all counts but I try not to put stuff in answers unless it's backed up by references. – Organic Marble Jul 17 '20 at 12:53
  • I think it would be relevant to mention how the Enterprise was actually flown. Was it mounted onto an airplane, flown to a high altitude, then disconnected for independent flight? – luther Jul 17 '20 at 19:23
  • @luther Welcome to the site! This site is a little different than many others on the internet. It adheres to a strict question and answer format, and isn't for discussions. The question here was, rightly, very specific, and got a very specific answer. Side issues such as you mention would not be an answer to this question. However, anyone can ask a question, and if you'd like to ask a new question about the drop tests, that would be great. There are a number of questions about the drop tests here already, search for the tag 'shuttle-carrier-aircraft'. – Organic Marble Jul 17 '20 at 19:28
  • @OrganicMarble: I have to disagree. The question is about how space-ready the Enterprise was. Discussing the full extent of its flight capability would, in fact, be a direct answer. Maybe there's some jargon there that I'm missing, but I don't see such a discussion in this answer. – luther Jul 17 '20 at 20:08
  • @luther It's always interesting to see the fresh viewpoints people bring to the site. You can, of course, write your own answer. – Organic Marble Jul 17 '20 at 20:15
  • My own comment was intended to get at what I think is the core of what the OP is asking. If I made my own question, it would just be restating this one. – luther Jul 17 '20 at 20:18
  • I did notice that. That doesn't mean we shouldn't make further comments or that you're not allowed to edit your answer. BTW, I'm not new to StackExchange. If there's a misunderstanding here, I can only guess it has something to do with terminology related to space exploration. – luther Jul 17 '20 at 20:27
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    @luther Thank you for the concern! I was however only asking about how/why Enterprise couldn't go to space, not about its usage inside the atmosphere. Your comments do raise the topic of dropping regular Space Shuttles from the carrier aircraft though! I just posted this question about that https://space.stackexchange.com/q/45416/29286. – Speedphoenix Jul 17 '20 at 20:59
  • @OrganicMarble, your answer does not address how Entreprise would have been on the pad or with the stack. Did it have the components needed like the other Shuttles? – Speedphoenix Jul 17 '20 at 21:00
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    @Speedphoenix sure, it could be mounted on the ET. It was used to fit-check the facilities. Here's a good artlcle with pictures showing it on the pad. https://www.nasa.gov/feature/40-years-ago-space-shuttle-enterprise-rolls-to-the-pad/ No main propulsion system plumbing though. – Organic Marble Jul 17 '20 at 21:03