Letter: Letter: Meant to miss

From PHILIP CLARK

I read with interest Peter Pesavento’s article ‘Two weeks that killed
the Soviet dream’ (18 December). Sadly one Russian claim in the article
– although basically repeated widely – does not stand up to analysis.

Once the L-1 circumlunar programme was acknowledged, Russian literature
has repeatedly claimed that Zond 4 was intended to fly around the Moon.
Pesavento repeats this claim, with a Russian source now claiming that the
reason Zond 4 went away from the Moon was because of a malfunction in the
attitude control system.

I hope to demonstrate once and for all that this claim is totally untrue.

The launch profile for Zond/L-1 missions called for the Proton booster’s
Block D fourth stage to shed its two ullage motors as the rocket stage/spacecraft
combination approached the equator northbound for the first time, about
an hour after launch. Over the equator the Block D would ignite for a second
time to place the Zond on its planned deep space trajectory and then separate.
Because the trajectory of Zond towards the Moon was relatively fixed and
the launch profile was also fixed, this means that the launch time was governed
by the position of the Moon relative to the launch site.

Looking at the known circumlunar Zond missions and also the Russian
unmanned Luna series shows that for a launch towards the Moon the lunar
Greenwich Hour Angle (GHA) is about 240degrees (there is a range of plus
minus 20degrees due to a variation in trajectories used, but the argument
still holds). When Zond 4 was launched, the lunar GHA was nearly 60degrees
and this clearly demonstrates that the launch time was carefully selected
for a flight away from the Moon. Any problems with the spacecraft itself
after launch are totally irrelevant to this argument – unless one wants
to claim that the spacecraft was accidentally launched either 11 hours early
or 11 hours late.

Phillip Clark Heston, Middlesex