When we think of rocket launches, most of us envision towering rockets many buildings tall, attached with various umbilical cords to a launch structure that provides access, fuel, data lines and electricity. And indeed, most rockets are launched that way — vertically.
One notable exception is the Pegasus launch system, which is launched from underneath an airplane — horizontally.
Here is how it works: A carrier airplane takes off from a runway. Attached to its belly or the underneath side of a wing is the Pegasus rocket — it looks very much like a large bomb that the jet is hauling along. The plane serves as the launch structure for the rocket, not only physically lifting it but also providing data lines. When the desired altitude is reached, the rocket is dropped — exactly like a bomb. After a few short seconds of freefall so the carrier plane can get out of the way, the rocket engines ignite and the rocket literally launches itself in mid-air. Directional wings focus the thrust downward while quickly orienting the rocket with the nose pointing upward, and off it goes!
It’s quite an ingenious concept if you think about it. You don’t need a dedicated launch pad — any runway long enough for your carrier jet will do, so no special infrastructure is required. A lot of fuel is saved by eliminating those first few thousand vertical feet of travel where the rocket not only has to overcome the highest gravity but also the densest atmosphere while carrying the heaviest weight. And if you’re launching your rocket into a near-equatorial orbit, the sheer speed of the airplane gives you an additional boost to go into orbit.
So, why don’t we launch all of our rockets that way?
You might have guessed that size has something to do with it. There are physical limitations to how much of an external load an airplane can carry — everything has to fit between the wing and the runway. So the Pegasus system is designed for smaller satellites and other orbital payloads. But if the shoe fits — wear it. To date, dozens of satellites have been sent into orbit that way. OK, so we don’t get any spectacular pictures and all the fire and smoke and thunder of a vertical launch, but it’s certainly a whole lot more cost-effective: A jet uses a lot less fuel than a rocket.
NuSTAR is an X-ray telescope that fits the bill for an air-launch. It is relatively small and lightweight, and unlike other X-ray telescopes of the past, such as the Compton or Chandra telescopes, NuSTAR is calibrated to work with rather high-energy x-rays — about the same as you would get at the dentist or the hospital.
In order to capture and image those x-rays, NuSTAR has to have a very large focal length. So, what’s that? In simplest terms, the focal length is the distance between a lens and a surface where it forms a sharp image. If you have a camera with a zoom lens, that’s exactly the same principle — the lens moves out of or into the camera housing in order to obtain a sharp image. You may also have seen those old-fashioned accordion-style cameras where you physically had to move the lens away from the photographic medium to sharpen the image — same idea. Except for NuSTAR, we’re not talking about a focal length of inches. The mast separating the “lens” from the “film” is around 33 feet long! At launch the whole thing was folded up tinker-toy like in a canister barely three feet long, and once in orbit, it stretched itself out to full length. With no atmospheric drag to contend with, a delicate structure like that works perfectly well in outer space!
So what exactly is NuSTAR looking for?
We can’t see Black Holes — their gravity is so strong that not even light can escape them. But as material is attracted and torn apart by its overwhelming gravity, it emits radiation, a good bit of it in the x-ray spectrum, and that’s what NuSTAR will look for.
At $180 million, NuSTAR is a bargain telescope — compared to the Hubble, or especially the James Webb, both of which run into the billions. And still, NuSTAR is expected to give us some spectacular images of our own galaxies and others around us. Granted, none of them will be actual photos as such — like at the dentist’s, the x-rays strike a receptor surface and those signals are interpreted by a computer near instantaneously to reveal your cavities in all their painful glory. The same will happen in NuSTAR — the data will be sent to ground stations and interpreted by computers, and then it will be time to ooh and aah over yet more spectacular views of the beauty of our universe — in a way we’ve never seen it before.
Incidentally, the principle of the mast is old hat to space buffs — it was originally developed for the Space Shuttle radar topography missions that took the most accurate measurements of the Earth’s surface ever — the radar device sat on the end of one such mast, and it worked extremely well. At only 770 pounds, NuSTAR is a wee little guy, but we expect a big bang for our buck nonetheless. Pun fully intended!
Read up on NuSTAR at its webpages at www.nustar.caltech.edu/
Beate Czogalla is the professor of theater design in the Department of Theatre and Dance at Georgia College & State University. She has had a lifelong interest in space exploration and has been a solar system ambassador for the Jet Propulsion Laboratory/NASA for many years. She can be reached at firstname.lastname@example.org.