Riding the strangest rocket in the world

凹凸曼

It's a curious beast, there's no doubt about that.

The Dnepr rocket that will carry Europe's ice explorer Cryosat into orbit next month is quite unlike most satellite launch systems.

But then most satellite launchers did not start out as nuclear missiles.

The Dnepr is one of those "swords into ploughshares" stories.

Under the terms of the Strategic Arms Reduction Treaty, a number of former Soviet SS18 ICBMs were decommissioned. Their atomic warheads were removed and their third-stages were modified to deploy spacecraft.

More than 40 satellites have now ridden the Dnepr into orbit. They launch from the famous Baikonur cosmodrome in Kazakhstan, and from the Dombarovsky base just across the border in southern Russia.

The company that markets the vehicle, ISC Kosmotras, has charged the European Space Agency (Esa) a little under 20m euros to send Cryosat on its way.

DNEPR LAUNCH VEHICLE

The Dnepr is a converted nuclear missile that is launched out of a silo.
BACK1 of 5NEXT I've attached a schematic to this posting to illustrate how the Dnepr launches.
It may seem a little bizarre, but the methodology is all driven by its nuclear heritage.

Essentially, the rocket is packed inside a canister which is loaded into a silo.

At launch, a black powder charge underneath the vehicle produces rapidly expanding gases that pop the Dnepr up out of the ground like a champagne cork.

There is then this heart-stopping moment when the vehicle just hangs 20m above the ground before the first-stage motors kick in and the former war machine climbs skyward.

You can see a youtube video of Dnepr launches here.

For Cryosat, the Dnepr is going up from Baikonur. It will fly south. Its first-stage will fall to Earth in Turkmenistan, another former Soviet republic. The second-stage will fall into the Indian Ocean.

It's then that something quite unusual will happen. When satellites are deployed by upper-stages, the normal practice is to use a spring mechanism to push them out in a forward direction.

The Dnepr is completely different. Immediately after the second and third-stages separate, the third-stage does a flip manoeuvre; and it flies backwards!



An artist's impression of Cryosat's rearward ejection from the Dnepr third-stage

A shroud that covers the satellite and protects it from the exhaust gases of those flipping thrusters is then jettisoned. It's at this point that the satellite is ejected. It gets chucked out the back, in the rearward direction.

Why? Well, Soviet engineers found this to be a highly accurate way to target nuclear warheads! Let's hope it works for Cryosat, too.

In getting the satellite into an orbit 720km above the Earth, the vehicle will be working at the limit of its performance. As you know, this Cryosat spacecraft is a rebuild of the mission that was lost on launch in 2005.


It means there is a little extra pressure this time. At Europe's Spacecraft Operations Centre (Esoc) in Germany, they will all breathe a huge sigh of relief when they hear the "acquisition of signal" alert go off in the control room.

It will mean Cryosat has been deployed and picked up by its first tracking station.

Cryosat itself has had an "interesting" build up to launch.

One key moment during final testing at Baikonur occurred when it was discovered that a broken ferrite fragment had stuck itself deep inside the spacecraft's transmitter equipment.

Had Cryosat flown with this debris in place, it would not have been able to send its precious ice mapping data to Earth.

You can listen to the extraordinary story of how the fragment was retrieved by clicking on the audio featuring Esa's Cryosat project manager Richard Francis.

It's quite a tale and involves a surgeon from a local Kazakh hospital with a bronchoscope, and some inventive engineers with a magnet on the end of a stick.


I'm pleased to report, though, that Cryosat is good to go. Thursday 8 April at 1357 GMT (1457 BST; 1557 CEST).

Watch this space.