The Smallest Orbital Rocket

The Lambda-4S rocket is currently the smallest (by volume) rocket ever built by humans that has carried a payload into Earth orbit. Much of its history is fascinating.

L-4s overview drawing

The lambda vehicle was 16.47 meters tall. It used all solid rocket fuel in four stages with two additional strap on boosters at launch. The entire vehicle weighed 9.4 tons (9399 kg) at liftoff. The final payload, a tiny test satellite named Osumi (おおすみ) weighed just a few kilograms.

Because it was all solid fuel the bulk density of the vehicle was very high. This meant it was narrower and smaller than any other (all liquid-fueled) orbital rocket of its time.

Size comparison to other small launch vehicles

Lambda 4S was almost completely unguided. This was in part because of the stigma attached to developing fully guided rocket systems so close to the end of WWII by an former Axis power. While Japan was occupied by the US it was entirely forbidden from any aerospace research or manufacturing. Compared to the Western powers it got a late start to the Space Race.

It’s not possible to put a satellite in orbit with no pointing assistance (i.e., purely unguided, ballistic flight) so the very last stage of the rocket had a special pointing device made up of a stable platform gyroscope and other sensors tied to a set of hydrogen peroxide control thrusters. After the third stage separated this device stabilized the 4th stage and aligned it to the correct attitude for orbital insertion.

Ascent profile and timeline

At 04:25 UTC February 11th, 1970 The Lambda 4S mark 5 vehicle successfully launched the satellite Osumi into orbit. The final motor cutoff was 8 minutes, 28.5 seconds after liftoff. It placed Osumi into a very high elliptical orbit (350 km × 5140 km). This was the first orbital launch for the country of Japan.


A history of the early Japanese space program and the Lambda test program

Digitized Data

Several old technical reports on the development and flight of the Lambda-4S are available. If possible the data from the papers have been digitized.

List of digitized datasets

Flight Simulation

Using those technical reports and the digitized data a reconstruction of the flight has been built in the JSBSim simulation framework.

Results of simulation