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Pakistan has ballistic missile capability

but they are using Chinese Long March-6 rockets and Chinese launch facilities to launch their moon orbiter.

I was wondering how hard it would be for a country to design a space launch vehicle if it already possessed ballistic missile capability.

What are the challenges for Pakistan in designing and deploying a space launch vehicle?

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  • $\begingroup$ Note that this is Pakistan ridesharing a Chinese moon mission, which is much harder conversion than ballistic missile into a LEO launcher. Possibly more relevant is their PAKSAT program which use used a range of commercial providers en.wikipedia.org/wiki/… $\endgroup$
    – GremlinWranger
    Commented May 5 at 11:25
  • $\begingroup$ Welcome to Space Exploration SE! I've adjusted your wording to make it a better fit for the site, and less likely to attract opinion-based answers. $\endgroup$
    – uhoh
    Commented May 5 at 11:34
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    $\begingroup$ A lot depends on whether they developed the ballistic missiles themselves or acquired the technology from somewhere else. $\endgroup$
    – Organic Marble
    Commented May 5 at 21:03
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    $\begingroup$ The propulsion system of the Ghauri-II seems to be based on that of the North Korean Nodong-7 missile, which delivers poor specific impulse, as discussed here: space.stackexchange.com/a/33728/195 $\endgroup$
    – Russell Borogove
    Commented May 6 at 2:03
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    $\begingroup$ For the record, "ballistic missile capability" isn't really a thing, because "ballistic missile" can refer to quite small rockets like a V-2 and its derivatives like Scud, or even rocket artillery systems that aren't remotely capable of leaving the atmosphere. Even the categories militaries use like SRBM or ICBM are kinda just arbitrary circles drawn around the range chart and don't take into account how big the payload is. $\endgroup$
    – Darth Pseudonym
    Commented May 6 at 20:25

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The first (and perhaps main) challenge is increasing the velocity of the payload. In a rocket system, the three techniques that are most commonly used to increase the payload velocity are:

  • Increase the engine's exhaust velocity (sometimes characterized as its Specific Impulse or $I_{Sp}$)
  • Reduce the rocket's structural mass (sometimes defined as the portion of the rocket's initial mass that is not the propellant expended during ascent and not payload.)
  • Add additional stages.

If the ballistic rocket (the heritage technology) is entirely based on solid rocket engines, these engines probably will not have high enough exhaust velocity to propel a rocket to orbital velocities, although, according to Wikipedia,

Solid rockets are suitable for launching small payloads to orbital velocities, especially if three or more stages are used.

If the goal it to launch larger payloads, a major challenge will be to develop more sophisticated rockets based on cryogenic liquid propellants. Since Ghauri-II is already a liquid-fueled rocket, Pakistan may already have developed this capability to some degree.

The next challenge is reducing the structural mass of the rocket. For example, if the heritage technology is based on steel, then the design team might need to develop the ability to manufacture a rocket out of lightweight aluminum-lithium alloys, like those used by SLS, Falcon 9, and Falcon Heavy. For example, steel's specific strength is ~63 kNm/kg whereas aerograde aluminum's specific strength is 204 kNm/kg. So, switching materials could reduce the mass by 63/204 = 1/3.24th, everything else being equal. However, this may involve mastering some more advanced manufacturing techniques such as friction stir welding and machining isogrids. It can be quite challenging to reduce the structural mass of the rocket while maintaining its reliability since the engineering factors (safety margins) for rockets are quite tight. Tory Bruno, when asked, replied that they are between 1.1 and 1.25.

If the heritage technology is a single-stage rocket, then an additional challenge will be to master multi-stage rocket technology, or more generally, the technology of "jettisoning parts on the way up". While this may seem simple, there are plenty of examples of rocket systems failing to get this right - at least not on the first try (e.g. Firefly, Terran 1, Rocket Lab, Starship IFT1). Since Ghauri-II is a two-stage rocket, Pakistan will have already made some headway on the journey to mastering this technology as well.

If they succeed in accelerating their payload to orbital velocity, the system will still need to execute a circularization burn to stay there. This will require the upper stage to be able to orient itself in the prograde direction while floating in a vacuum, somehow settle the propellants in the tanks, and finally relight its engines. None of these are trivial problems. Short to medium-range ballistic rockets likely would not trail-blaze these capabilities much.

These days, the upper stage should also perform a second de-circularization burn (see dot at top-right) after releasing its payload(s), to help keep the amount of orbital debris at manageable levels. enter image description here

This is not a complete list of all of the challenges, but it should provide a general sense of the kinds of problems remaining for Pakistan to solve.

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    $\begingroup$ Note that the Ghauri series seems to have been developed with North Korean missile technology, derived in turn from Soviet Scud missiles. Their liquid-propellant engine uses non-cryogenic propellants with poor specific impulse. $\endgroup$
    – Russell Borogove
    Commented May 6 at 2:06
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    $\begingroup$ Thanks for the additional info! I wasn't sure, which is why I added: "to some degree". $\endgroup$
    – phil1008
    Commented May 6 at 3:15

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