Pushing the Envelope
Pushing the envelope
Throwing satellites into orbit
Robert Coppinger
The history of launching an object with a sling is literally biblical, with David’s successful strike at Goliath. The Roman Empire had catapult siege machines to launch a destructive mass at an enemy. Both sling and catapult follow the principle of stored energy released and converted into energy of motion which is transferred to the missile. When it came to space launch, the earliest ideas took their inspiration from the cannon. What Jules Verne’s huge cannon in his book, From the Earth to the Moon, does have in common with the sling and the catapult is ballistic trajectory. These are referred to collectively as kinetic launch systems.
In October last year, the sub-orbital kinetic vertical launch of a projectile was claimed by California-based firm SpinLaunch. Started in 2014, SpinLaunch aims to launch small satellite constellations into low Earth orbit with no rocket.
SpinLaunch’s launch facility is in New Mexico and the company plans to serve customers from 2025. Airbus’ venture arm, Airbus Ventures, has invested in SpinLaunch, along with Google Ventures and venture capital firm Kleiner Perkins. In 2019, SpinLaunch was awarded a responsive launch prototype contract from the US Department of Defense’s Defense Innovation Unit. That unit deals with commercial outfits that can provide solutions to challenges the military has. The solution the military wants is a rapid, low-cost responsive satellite launch to replace those rendered useless by enemy action. Kinetic launch systems have been discussed as a low-cost launch method in academic papers for decades. Derek Tidman, a UKeducated physicist, promoted his ‘Slingatron’ concept in the early 1990s which could send tonnes of payload into orbit. Tidman received funding in the 1990s for a NASA/US Army project to develop his Slingatron idea. Tidman’s ideas included a super-conducting levitation acceleration system.
Another kinetic launch concept is the ‘centrifugal launcher’ or ‘sling rotary launcher,’ described in the 2006 book, Non-Rocket Space Launch and Flight by Alexander Bolonkin. In Bolonkin’s book he proposes a ‘space projectile’ system with an 8-ton (7.25 tonnes) payload capacity which uses an open-air sling rotary launcher that needs carbon nanotube materials for the cable’s required strength and elasticity.
Bolonkin also proposes a human space launch system where a spacecraft is attached to an aircraft by a nanotube cable and rapid circular flight generates the energy to fling the released spaceship into orbit. A G acceleration level of 7.8g, for a few seconds, is considered acceptable by Bolonkin for the human occupants.
SpinLaunch’s system is very different and looks similar to Tidman’s concept, a circular acceleration system in an airless tube with a vertical exit shaft. The same year Bolonkin’s book was published, Tidman created a website, slingatron.com to promote his launch system and in November 2007, Tidman published his own book, Slingatron – A mechanical hypervelocity mass accelerator. One similarity Bolonkin’s concept does have with SpinLaunch is a composite carbon fibre tether to spin the payload. The tether spins the payload, missile, in a vacuum to avoid heating, and when it does leave by the exit shaft, the tip of the missile acts as a heat sink to absorb the heat from the momentary atmospheric impact and ascent friction.
SpinLaunch’s sub-orbital facility uses a thin cover at the top of the exit shaft to keep the circular chamber’s vacuum intact until the missile breaks through the cover to ascend. The missile creates a sonic boom upon its exit which SpinLaunch states follows the payload upwards. SpinLaunch’s sub-orbital launch facility in New Mexico is a test bed for the planned orbital system which will use high-speed airlock doors at the top of the exit shaft. The first-generation SpinLaunch system is planned to have a 200kg payload capability. This mass is considered a small satellite and spacecraft of this size have been used for Earth observation, telecoms and in-orbit technology demonstration. SpinLaunch could send up replacement spy satellites or spacecraft with other military functions.
The trend for satellite launch has been for more small satellite launch providers that use austere launch sites and expendable 3D printed rockets, and air launch from aircraft. Kinetic launch systems require a high level of investment in a single location and have a limited range of orbits they can deliver to. What will be SpinLaunch’s final trajectory?