When we talk about communication satellites, we sometimes mention that each is roughly the size of a school bus. That provides a bit of scale, and suggests how difficult it might be to launch it into orbit.

But it would still be nice to see a real example for an even better understanding of its size and bulk. There are occasional prelaunch photos of bunny-suited workers prepping one for launch, but it’s hard to relate to human sizes in that sterile environment.

Now we’ve got an alternative. One of the first Sirius radio satellites was donated by SiriusXM Radio and Space Systems/Loral to the Smithsonian last week. The Sirius FM-4 broadcasting satellite was a backup for its three working satellites, which covered the US in an inclined elliptical orbit. The FM-4 satellite will be on display in the James S. McDonnell Space Hangar of the National Air and Space Museum’s Steven F. Udvar-Hazy Center.

“The availability of a flight unit like Sirius FM-4, which was never launched, is extremely rare and will be a significant addition to the museum’s collection,” said Martin Collins, space history curator.

John Celli, president of Space Systems/Loral, said, “It is an honor to participate in the donation of the original spare satellite, which we are pleased to say was never needed.”

The National Air and Space Museum’s Steven F. Udvar-Hazy Center is in Chantilly VA near Dulles International Airport. Next time I’m traveling through, I’ll try to make time to take a look. Too bad they probably won’t let me touch it, even if I wear a bunny suit.