Rockets of Today

SPECTRUM — Germany

The Spectrum is a two stage launcher being developed by a startup in Munich named Isar Aerospace, which takes its name from a river that flows through Bavaria. So they are not far from their rivals Rocket Factory Augsburg, and the two are planning to launch out of the same little spaceport on the island of Andøya, Norway.

The rocket itself is generic by modern standards, with just one unusual feature, which is that the fuel is propane. Their stated reason for this is its “density specific impulse”... and I’m not sure what that exactly means but it may mean that they chose it for having a higher exhaust velocity than kerosene while using a smaller and lighter tank than liquid methane. It burns pretty cleanly too, and should not be too difficult to ignite in a vacuum. And it won’t need a lot of extra purification like kerosene does.

Like plenty of other recent rockets, including RFA’s design, the first stage has nine engines and the second has one. As far as I can guess from their promotional guff, these engines are conventional gas generators. (Why don’t we see rockets with seven engines instead of nine? That would probably be a better balance between lower and upper stage thrust needs. The only seven engine designs we’ve heard about are the Tianlong and the New Glenn... and the Tianlong in its initial version only has three engines instead of the seven they talked about, and the New Glenn does not use the same engine, or even the same fuel, on the second stage.) RFA says the engine has high pressure. The second stage engine is restartable.

The fairing size is two meters and the capacity is one ton — a very popular size with rocket builders these days, though I’m not sure a lot of satellites are that size. They intend to launch in 2023, but we’ve heard that song before.

Spectrum: mass unknown, diam 2.00 m, thrust unknown, imp unknown, gas generator? (propane), payload 1.0 t, cost unknown.