Skip to content

Using Outlook from orbit

How does the Space Shuttle crew use Microsoft Outlook?

On the Space Shuttle and the International Space Station they use Microsoft Outlook 2003, but not quite in the same way that us earthbound Earthlings do.

The space shuttle Atlantis is orbiting the earth right now and the crew exchange emails with the ground a few times each day. Bandwidth is a constraint and you don’t want the busy crewmembers bothered with spam or unnecessary messages so NASA has a special system in place.

The crew use fairly standard laptops running Microsoft Outlook (currently Outlook 2003) with Exchange Server as the email host, but they don’t link to the server using any of the standard methods.

Instead of exchanging messages one-by-one via a network link, all incoming and outgoing messages are bundled up in a file. That file is moved from ground to orbit and later back again.

A few times each day, NASA uploads a small .OST file for each crewmember. An OST file is like an Outlook PST file and contains all the Outlook data. Normally an OST file has all your email, calendar contacts etc but for shuttle crew the OST is just a container for exchanging groups of messages.

For shuttle crew, all the OST contains is incoming email (the Inbox) with all the new email in it. These OST files are tiny by ground-based standards – around at most 4MB for shuttle crew.

If you listen to the shuttle communications on NASA TV you’ll sometimes hear ‘Go for Outlook’ – that means there’s new email (in OST files) uploaded for the crew.

The crew open their copy of Outlook and see the new email. They reply or compose new messages which go into the Outbox also stored in the OST file.

Any email the crew want to keep they have to copy to local Outlook storage on their laptop – in other words a PST file. Here’s our mockup of how the Outlook folder list might look with the OST storage folders under ‘Mailbox’ and the local computer PST file under ‘Laptop Storage’

Outlook 2003 - mock-up of space shuttle crew folder list image from Using Outlook from orbit at

The OST file, now with outgoing emails, is copied back to NASA on the ground where the messages are sent, copied to the Sent Items folder and any new email is placed in the OST ready for the next upload.

Because there’s limited bandwidth up to the shuttle it’s important to keep the OST fairly small so occasionally you’ll hear NASA controllers ask the crew to clean out their Outlook files (the OST).

You might also hear ‘CapCom’ asking the crew to shut down their copies of Outlook so that an OST transfer can occur. Outlook puts a file lock on any PST/OST file which prevents any copying (a problem anyone trying to do an Outlook backup might be familiar with).

This sounds cumbersome and messy, it’s certainly not the way you’d do it here on the Green Hills of Earth. However it makes sense for NASA given the bandwidth constraints and especially time management for the crew. Shuttle crews have very busy schedules and you don’t want them wasting time with unnecessary emails. NASA has apparently decided that the time they spend moving items from the OST to PST is worth it compared to other options.

In addition, communication with the ground isn’t always possible (you’ll hear warnings of LOS – Loss of Signal during mission communications) so standard methods of email transfer like POP/SMTP, IMAP etc might not be reliable.

Back in the days of the Apollo missions there was no email, in fact no way to transmit data to the Command Module except voice. Any changes in procedures or reprogramming the (by today’s standard) primitive computers had to be done by the astronauts taking careful dictation from Houston then reading it all back to double-check.

Using OST files for transfer means that NASA uses Microsoft Exchange Server for email communication. It’s surprising that Microsoft hasn’t made more noise about the use of Microsoft Office in space.

Emailing the Space Shuttle

You can’t. Shuttle crews are incredibly busy and have much better things to do than deal with anything that might distract them from the many tasks at hand.

We suspect that one reason for the OST transfer method of sending up new messages is so that someone on the ground can discreetly and personally check all messages going to orbit. Spam could be axed and maybe low priority messages are sidelined until the crew returns to earth.

International Space Station

The International Space Station – ISS crewmembers use the same Outlook system with OST files being transferred a few times each day.

NASA tells us the only major difference is that the OST files can be comparatively larger, up to 30-40MB since the ISS has better bandwidth connections.


You can follow the activities on the latest shuttle mission live on NASA TV. Some cable companies have NASA TV or you can live stream it to your computer. Office Watch ‘comedy central’ always has NASA TV running in the background during missions. Between more mundane pursuits we can glance at the video and see amazing things being done, live, a few hundred miles above our heads.

We’d love to report that we tried this email system ourselves in the shuttle but instead our thanks to NASA Public Affairs for their help in preparing this piece.

About this author