The Soviets had only one flight on the board for 1970,
Soyuz 9, which launched on June 1. In mid-April, mating up of the rocket stages was likely just getting into gear.
Dramatic license could alter that date.
More to the point, even if they had, what could they have done?
More than you give them credit for. For a start,
soyuz was designed to be flown from the ground, and docked with a target automatically. For another,
they had plenty of other rocket available. The soviets also had
practical experience with docking.
None of this would be of assistance to the OTL NASA plan, so for a story where the soviets did help, we'd need to force a change the NASA rescue plan. I'm not going to work out the maths for the following. I'm just going to assume it's completely ASB and live with it...
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Soviet Rescue!Apollo13
The explosion occured on the way to the moon. Early fears as to damage wre soon put to rest, but then replaced by much worse fears. The Service module and engine were largely intact, but the heatshield was not. It woudl be qie possible for the crew to make it to the moon's surface. They'd just not be able to return home.
This was considdered an unacceptable outcome, and thus NASA started to considder idead further down the slush pile, until they reached a idea based on the work of Phil Bono. He suggested that rocket exhaust gas (while not good for a rocket's structure) can be used to shield a rocket from the higher temperature plasma generated by reentry; if that rocket was basically flown backwards.
The Service Module lacks the DeltaV to break into Earth orbit, even if the Luna module is used for a Direct return burn on the far side of the moon. But could it have enough rocket fuel to protect the service module during an aerobreak manouver through the upper atmosphere?
'Damned if we know,' come the answer. The engineers could do the maths, which said teoretically yes, but had no way to test how that translated to reality. 'Possibly. Flip a coin.'
'Does anyone have any better ideas that do NOT involve certain death?' Silence. 'Well then...'
The decision is made, and the Soviets have a brown trouser moment when the Americans call them back, and say, 'Actually, now that you mention it...'
NASA doesn't need a full souz. All it needs the service module and reentry module (with
three seats if you please), mounted in any way possible into any rocket, and placed into a stable orbit and attitude close to Apollo 13 - assuming it survives. Oh yes - and one more thing, it needs to have an American hatch from a Lunar lander wielded to the front, so it can serve as a docking target.
Yes we are quite serious. No we have not been drinking.
The russians (knowing how it will look if three US astronauts survive intoLEO, only to be killed by russian tardiness) move heaven and earth to get their most flight ready rocket (OTL Vostok/Kosmos 331) on the launch pad, and put together the flight team needed to do this on the fly with no preperation what so ever.
And they both pull it off by the skin of their teeth. The service module is heavily damaged by it's trip through the atmosphere, but somehow survives. The Russians launch their rescue craft, and it gets close enough for the Americans to dock on their second try, after a terrifying aborted first attempt.
Under Russian ground control they reenter in shirtsleaves, and land in Kasakstan, located by the russians two hours later. They are greeted as war heros, blessed with medals and kisses, and then flown to Moscow to meet the Premier, before being handed over to the US Ambassador at the airport.
And then six months later both nations are back to suspiciously peering at each other over the trenchtops, and over the no-mans-lad of Europe.
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And once again, yes I am aware that the last paragraph is the most realistic aspect of the entire scenario. But, you know, for fun!
