Earlier this month, ten Cubesats – small, cheap satellites weighing around a kilogram each – were launched into orbit. With nearly 1,500 of these tiny satellites launched so far, adding ten more might seem trivial. However, this wasn’t an ordinary start.
Instead of lifting off the ground, these NASA satellites launched the rocket under the wing of a modified Boeing 747 called Cosmic Girl. The plane carried them to an altitude of 11 km before the missile was fired.
This marked the first successful launch of Virgin Orbit’s LauncherOne rocket, which marked the beginning of its commercial ventures. The company hopes to offer affordable, flexible satellite launch services without having to use on-site locations.
But how does it actually work to launch a rocket from an airplane?[Read: How much does it cost to buy, own, and run an EV? It’s not as much as you think]
She is just a cosmic girl. Virgin Orbit / Greg Robinson, CC BY
Take off from an airplane
Typically, a missile launched from a launch site on the ground consists of two or three stages that allow the missile to lose weight as it consumes fuel. The first stage is the part that ignites on launch and propels the missile from the ground. When the rocket reaches a certain altitude, the first stage separates and the second ignites. A third stage works on the same principle and usually places the payload – the part we want to put into space – in its final orbit or interplanetary trajectory.
When satellites are launched from an aircraft, the carrier aircraft acts as both a launch site and a reusable first stage of the rocket.
Airplanes are more efficient than missiles when they take off from the ground, but without an atmosphere they cannot generate aerodynamic lift. Air launch takes advantage of this by attaching a missile to an aircraft and releasing it at high altitude.
Aircraft take-offs not only save fuel, but also offer other benefits. Conventional rocket launches are often repeatedly delayed by poor weather conditions. It is easy to change take-off locations with an airplane as it can take off from a commercial airport. Annoying weather conditions can simply be flown around and different launch requirements for different spacecraft can easily be accommodated.
The payload. Virgin Orbit / Greg Robinson, CC BY
There are Limits
Of course, air launch is not a perfect solution. The size of the missile is limited to the carrying capacity of the aircraft. A dedicated carrier aircraft can potentially carry much more, but there is not much headroom for larger launch vehicles right now.
Stratolaunch, the developers of the giant carrier aircraft of the same name, which can carry a rocket weighing 250 tons, abandoned its program of launchers for heavy loads in 2019. For comparison: LauncherOne weighs 30 tons and is only used to transport small satellites.
Launching a rocket 10 km above the ground saves some fuel, but most of the fuel needed to reach orbit is not in altitude, rather it is moving at enough speed for it to fall into orbit. While an aircraft’s airspeed can make a small contribution to this requirement, the fuel savings from air take-off are not as high as it may initially appear.
A relatively small launcher, LauncherOne, has the capacity to put 500 kg into near-Earth orbit. Heavy-duty launchers like Ariane, Delta and Falcon can launch many times this weight and continue to be used for large satellites and interplanetary missions.
But Virgin Orbit doesn’t target big, expensive launches. With small satellites, cubesats, microsatellites and nanosatellites, all of which are rapidly being adopted by the space industry, air launches could mean a significant improvement in versatility and, most importantly, cost.
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The idea of air launch has been around for some time. Nasa launched a Pegasus missile from a B-52 bomber back in 1990. The Pegasus launch service is still operational and has completed 39 successful flights. The launches are expensive, however, and only four have been done in the past decade.
There are already several short-term start-up contracts. In the longer term, there are plans to add a third stage to the LauncherOne rocket, with which smaller satellites – around 50 kg – can be brought into distant orbits in order to fly past Mars or Venus.
Not many other air launch programs are in development. SpaceX abandoned an air-launched variant of the Falcon back in 2012. The Pegasus launcher still exists but has not been launched since 2019.
The British aerospace company Reaction Engines aims to fully combine aircraft and spacecraft with the SABER engine, which can act as a jet in the atmosphere and a chemical rocket in space. However, this project has been delayed several times and may still be a long way from its first commercial launch.
As the provision of launch services moves more and more into the private sector, LauncherOne has to make a business case to survive in an increasingly competitive market. There aren’t many direct competitors for small single launches like Virgin Orbit’s, though heavier launchers from more established companies like SpaceX can compete by launching multiple small payloads on the same rocket. It remains to be seen whether the versatility and relatively low cost of the system will prevail.
This article by Simon Lindsay, a researcher in the Faculty of Physics and Astronomy at Leicester University, is republished by The Conversation under a Creative Commons license. Read the original article.
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