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Choice of launcher seems to be an early decision in the design of spacecrafts. There would be an advantage to having the option to easily change launcher, especially for an interplanetary mission with a rarely recurring launch window, in case the intended launcher is grounded for a long time. A mission prepared to deal with an emergency, such as a space tug to save a failed orbital insertion of a crewed or otherwise valuable spacecraft, or for last-minute deflection of an asteroid, would also benefit from being able to launch from any out of several frequently launched rocket types (replacing the payload of the next one prepared to go).

The most frequently launched rockets nowadays are Atlas V, Falcon 9, Ariane 5 and Proton (assuming that Soyuz is too feeble). Incidentally, two of them have been grounded for 4 and 7 months now.

  • Could one design a spacecraft to go with at least three out of these four?

  • Would it need a bulky adapter stage?

  • Could one make adapters that could take almost any satellite or spacecraft on any of the launchers? (To steal the competitors' customers)

  • Proton is horizontally integrated, the others vertically. Is that outright disqualifying for inter-launcher payload compatibility?

I suppose one "could", and that it comes down to how much would it would cost in mass and extra engineering. If it would be cheaper to have a dedicated launcher on some level of standby instead.

Delta IV and the Japanese H-IIB are AFAIK both based on Delta, so they might be quite compatible. However, they are the most expensive launchers and do not launch very often.

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    $\begingroup$ F9 is horizontally integrated. $\endgroup$
    – Russell Borogove
    Commented Jan 4, 2017 at 11:10
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    $\begingroup$ The payload to LEO of these rockets is about to 20 metric tonnes, but the payload to GTO is only 3.2 t for the Proton and about 8 t for the other launchers. If these numbers are correct, the Proton may be used only for smaller GEO payloads. But what about the available space inside the fairing of these rockets, the maximum diameter and height of the payload? $\endgroup$
    – Uwe
    Commented Jan 12, 2017 at 16:40

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The physical adapter is the easy part. These have standard dimensions. Commercial launch providers were quick to realize it'd be advantageous to offer compatibility. E.g. the Ariane 5 payload fairing dimensions were based on the Shuttle payload bay.

Looking at the user manuals for various launchers, you can see the differences:

  • vibration and other environmental factors (a satellite has to be tested and qualified for the launcher environment, so you have to budget for more tests)
  • maybe: electrical interfaces, although there are commonalities here too, for example the Ariane 5 and Falcon 9 use the same electrical connectors between launcher and satellite. I haven't had time yet to do a thorough comparison.

So provisionally: yes, you should be able to design a payload that's compatible with multiple rockets, without too much of a mass penalty.

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Changing launchers late in the development cycle is unusual, but it does happen. For example, the next Cygnus mission (OA-7) has been moved on to an Altas 5 from Antares in order to carry more cargo.

In this case, it appears that OA and NASA made the decision to switch simply because the Atlas 5 can carry more mass to orbit. The Cygnus missions OA-4 and OA-6 also launched on Atlas, and the more powerful launcher enabled those missions to carry better than 2000 kgs more payload mass to ISS than the missions launched on Antares. It's desirable for OA-7 to do the same because of timing: both JAXA and SpaceX have experienced delays in their resupply contracts recently.

As Hobbes hints in his answer, the biggest difficulty in switching launchers is that nearly everything will need to be requalified. NASA requirements are exacting, but even fully commercial launches must convince their insurers and government regulators that their payload will not cause a hazard during launch - and in Cygnus's case, it also can't cause a hazard to ISS.

Everything from the structure to the software must pass qualification tests, and these tests are expensive in both time and money to perform (months of time and thousands of man hours, speaking from experience). It isn't worth the expense to do for other launchers, which is why you're unlikely to see vehicles "designed for three of the four", as you put it. That said, if there's a legitimate need to switch, it's certainly possible - engineers are pretty resourceful.

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In response to the part of the question "Could one design a spacecraft to go with at least three out of these four?" the answer is yes.

This "standardised" situation I've described is probably more specific to GEO communications satellites where the main commercial platform designs are already structurally qualified for the main launch vehicle choices. Even in this context there is a lot to do in terms of routine analysis effort and perhaps changes that need to reflect:

  • The specifics of each type of payload in terms of its mass and thus LV performance impacts
  • The vibration spectrum of each launch vehicle option that is cascaded down to mission specific components
  • The couple loads analysis — most relevant for any unusual items such as folded antennas
  • The stowed accommodation inside the fairing for each LV type
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The launcher is chosen early is that once you know what launcher you intend to use, then you can determine how big (in particular how heavy) your satellite can be. That would have a BIG impact on the design of the satellite. I'm pretty sure that there have been times that a mission has had to change to a larger (typically more expensive) launcher because the satellite was too heavy, but can't come up with a reference right now.

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