Aerospace and Electronic Systems Magazine October 2017 - 12

Current Use of Linux in Spacecraft Flight Software
try. It seems likely that use of Linux in spacecraft flight software
will continue to grow, driven by the following factors:
1. Increasing complexity of demands placed on the flight software requires reuse of existing software modules, tools, and
processes.
2. Computing power continues to become cheaper and is requiring less power, reducing the need for detailed optimization of
software.
3. Skilled labor familiar with Linux-based mobile development is
available more readily than RTOS developers
However, the hard real-time suitability of Linux still remains
questionable; while we have described some possible solutions,
there is no de facto standard way of making Linux hard real-time
compatible. However, SpaceX has demonstrated with their Falcon
9 rocket that Linux can be used very well in hard real-time systems.
Linux will not be the solution for all systems; some are still best
written at low level without OS. Bringing Linux to the embedded
platform allows utilizing the huge catalogue of Linux-compatible
software developed during the past decades. This benefit must be
weighed with the real-time considerations.
If Linux is to be used, hardware needs to be capable of running
it. COTS hardware, due to its prevalent use across all industries,
evolves much faster than the so-called space-grade or radiationhardened hardware. Consumer electronics win in all performance,
power consumption, and size categories; robustness, durability, and
radiation tolerance is where "traditional" space hardware stands
out. However, redundancy can be used to build robust systems
with off-the-shelf electronics by duplicating the hardware components, or in case of Planet, by duplicating the satellites themselves.
Using Linux in space does not necessarily differ much from
many terrestrial applications, and much "terrestrial" software and
utilities can be reused for space applications. Many problems encountered during development may already have been solved, and
the solution may be available as open source.
The ease of deploying Linux may be deceptive: it may be relatively easy to get the Linux kernel to boot on the target platform
and some applications running, but deeply understanding the kernel well enough to use Linux in safety-critical software is a much
bigger effort. Linux is complex, and systems built on Linux will be
complex, and thus hard to test. Quality assurance remains important in preventing even simple problems such as the LightSail-1
disk overflow problem already discussed. Some systems may be
quick to develop with Linux, but very hard to test; on the other
hand, the same systems could be written from ground up with the
same effort, and very easily tested. The difficulty of verifying and
validating Linux-based systems is probably the reason for its current nonadoption in traditional space industry avionics.

development tools, large user community and pool of developers, deployment across several industries thus leading to off-theshelf availability of many utilities and software, and support for
many types of hardware. Platform-independent, Linux-targeted
software could even be developed and used across various missions.
However, before Linux is to be used, questions that need to
be considered include limiting hardware selection mostly to 32-bit
and 64-bit architectures, uncertain and unstandardized hard realtime capabilities, and the possible presence of unused software
modules that only consume resources without additional value.
It is likely that the use of Linux in all kinds of spacecraft will
continue to grow. SpaceX and Planet have already commercially
proven that Linux can be used equally well in all categories of
spacecraft: launch vehicles, CubeSats, and, in the future, manned
spacecraft. Thus Linux software could be traded between spacecraft, and everything "terrestrial" developed for Linux can also be
taken into space with very little effort. The popularity of Linux
is possibly one of the greatest reasons why it will continue to be
taken to space.

REFERENCES
[1]
[2]

[3]

[4]

[5]

[6]
[7]

[8]
[9]

CONCLUSIONS

[10]

This article discussed the use of Linux in spacecraft. Several cases
found in literature were presented and studied.
It was found that Linux has several benefits for spacecraft
software development, including availability of source code and
12

IEEE A&E SYSTEMS MAGAZINE

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OCTOBER 2017

http://www.extremetech.com/extreme/155392-internationalspace-station-switches-from-windows-to-linux-for-improved-reliability http://www.extremetech.com/extreme/155392-internationalspace-station-switches-from-windows-to-linux-for-improved-reliability http://dx.doi.org/10.1109/AICCSA.2009.5069315 http://dx.doi.org/10.1109/AICCSA.2009.5069315 http://www.linuxjournal.com/article/7767 http://www.geosci-instrummethod-data-syst.net/2/121/2013/ http://www.geosci-instrummethod-data-syst.net/2/121/2013/

Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine October 2017