Air-launch of nanosats for space development

[Note: This was written for the Kickstarter campaign of Project Spartan Spear, and appears there as Update #4.]

Exploration and settlement of the solar system are throttled by the cost of missions and availability of technology. Traditionally, this has restricted participation to governments and large companies.

However, experience in technology sectors such as consumer electronics shows that innovation often comes in rapid incremental steps. New products are deployed on an annual cycle. But internal prototype builds of software or hardware may happen on the scale of weeks, or perhaps a few months.

With large spacecraft and high launch costs, there is little room for prototypes, and very little flight experience with a system before it is selected for a mission. Small incremental steps are virtually impossible. This pushes up the cost of development and test leading up to launch. The mission becomes more expensive and more averse to risk. Thus, there is strong preference for systems with flight heritage; that is, a system that has flown before in space and successfully proven itself.

Spartan Spear represents a way of breaking though the roadblocks to flight heritage.

CubeSats

In the past 15 years, CubeSats have become a de facto nanosatellite standard for delivering small payloads to space. The typical life-time is weeks or months. The instrumentation in the CubeSat usually consists of commercial off-the-shelf parts rather than space-rated radiation-hardened parts that are expected to last several years. With increasing capability that follows Moore’s Law, CubeSat payloads now have computing and sensor capabilities that personal computers did not have a decade ago.

The cost of a CubeSat is miniscule compared to an advanced NASA science mission. To be fair, advanced science missions do a lot of things which commercial markets don’t think about. However, many of these may benefit from some level of incremental development using CubeSats.

Although CubeSats would be ideal platforms for proving new space technologies, there are limits imposed on what a CubeSat can accommodate. These are dictated by how they get to orbit.

  • They may be bundled as secondary payloads along with a more expensive primary payload which pays the bulk of the launch costs.
  • They may be transported as cargo to the ISS, entering crew-occupied areas, and launched from there.

Due to the cost of the primary or because astronaut lives are at stake, the design and capabiliities of the CubeSat are very restricted. For example, in most cases, propulsion technologies are not allowed. Movable parts must be shown through analysis that they will not accidentally break apart, and float into crew areas and get ingested into equipment. There is no room for small particles or dust; astronauts do not like to breathe them or get them in their eyes. To broaden their capabilities, CubeSats need to be broken out of secondary payload status.

Making CubeSats into primary payloads requires a different kind of launch vehicle.

Launch vehicles

In the past few years, NASA and DoD have recognized the need for launch vehicles that focus on nanosatellites. They have provided research money and technical advice to some small firms to develop their concepts further and push toward viable hardware.

More recently, DARPA has launched major initiatives for rapid air launch. One program aims at rapid response to put small satellites in orbit; for example, a small tactical satellite might be launched within 24 hours of call-up to support operations on the ground. Another program aims to develop spaceplanes which can fly to Mach 10 and launch satellites on a daily basis.

There is also an emerging industry for asteroid mining which will depend on scouting near Earth asteroids (NEAs), which are usually only seen a few days before their closest approach to Earth. In effect, a nanospacecraft needs to be launched within days of spotting an asteroid.

However, there are currently no small launch vehicles capable of rapid response to put Cubesats or other nanospacecraft into Earth orbit or beyond. Large aerospace companies generally don’t build small rockets for satelite launch or small engines that they would need.

Spartan Spear

The Spartan Spear vehicle is an air-launched rocket that is ideally capable of rapid response, but certainly one where rides could be booked weeks, if not days, in advance. A new engine is being designed to put 1U and 3U CubeSats into low Earth orbit. (This is the point of the Kickstarter campaign.)

Because the Spartan Spear rocket is air-launched, it differs from ground launch in many ways:

  • The initial rocket engine performance is closer to space flight. (Atmospheric pressure is about 1/10th of what it is at sea level.)
  • The initial speed of the rocket is that of the aircraft.
  • Launch can take place over water, far away from populated areas or industrial facilities.
  • The efficiency of aircraft engines in terms of necessary propellant far exceeds that of rocket engines.
  • The aircraft constitutes a recoverable initial or zeroth stage.
  • The ground support facility for launch is an existing airport rather than a custom-built launch pad.

There are still issues which may constrain take-off to a limited number of airports, but the impact should be nothing like a launch pad. Furthermore, there are several regional governments or business interests that are preparing spaceports for launch by air or balloon, but not ground-based launch pad.

Accelerating flight hardware maturity

The ability to put CubeSats in orbit on a weekly or nearly daily basis means that labs or small companies developing new technologies for space can employ an iterative cycle of product development:

  • Prototypes can be built and launched.
  • Performance and measurements can be analyzed.
  • Design improvements can be incorporated.
  • An improved prototype can be built and launched.

Depending on the pace of the business, this may take place every few weeks or every few months. More importantly, personnel do not have be shifted to another project, only to be brought back a year later for the next phase, and disrupting the project they were pulled from. In effect, incremental space development starts to make business sense.

With this sort of cycle, hardware for space flight can be matured far more rapidly than when the CubeSat has to be a secondary payload. As primary payloads, CubeSats can open up the test and demonstration envelope for small propulsion, materials in space, effects of space flight on plants and microorganisms, etc.

When testing hardware, rapid iterative development with CubeSats hastens the ability to build flight heritage, the key bottleneck that keeps new technology from being adopted on space missions.

Among its purposes, the Spartan Spear vehicle is intended to facilitate this rapid cycle. The main engine being designed for Spartan Spear is a critical first step in bringing the vehicle to reality.


Revision history

  • 2015-02-22: original post on “rocketscirick.com”, copied as Update #4 of Kickstarter campaign for Project Spartan Spear.
  • 2014-02-26: small fixes – 3 word edits or typos.