April 15^th, 2001

Spaced Out

There was no fanfare and the spectators were thin to non-existent. There was sporadic news coverage on TV, but most viewers flipped channels to look for soap operas. STS-110 was just another boring non-event.

Yet the sight was just as spectacular as ever. As the countdown droned down to zero, engines ignited, a roaring cloud of fire and smoke emanated from under the stately but huge, torpedo-looking craft, shattering the silence under the deep-blue sunny Florida sky. Powered by some of the most powerful solid rocket fueled engines in the world, space shuttle Atlantis gracefully lifted off from the Kennedy Space Center, at 3:44 PM, on Monday April 8^th. This mission is the 109^th liftoff of the space shuttle and is officially known as STS-110 (Space Transportation System, flight 110; the STS number do not quite correspond to the sequence of flights). Since the 109^th flight is still in orbit, the space shuttle program has executed 107 flawless landings so far.

STS-110 is just a faint shadow of the excitement and media circus that surrounded STS-1, the maiden voyage of the first space shuttle Columbia. With two astronauts onboard (Young and Crippen) and uncountable people jostling for a glimpse, Columbia was NASA’s first reusable, land-landing space vehicle, which lifted off at 7:00am on April 12^th 1981.

The launch of Columbia was a jewel in NASA’s crown, 12 years after the magic of the first moon landing (July 1969). The space shuttle program was initiated to create a general-purpose space transportation vehicle for a multitude of research, exploratory and utility purposes. The shuttle missions have been used to place communications satellites in orbit, assemble the space station, launch and subsequently repair the Hubble Space Telescope, launch the orbiting Chandra X-ray observatory and conduct a myriad of experiments in space. 

Columbia has been flying since 1981 and has completed 27 missions. In 1983 a new shuttle, the Challenger came on line. The 12^th mission for Challenger (25^th for the shuttle program), called STS-51L started on a beautiful day in January 1986. It was a picture perfect takeoff, watched by millions on live-TV worldwide. Shuttle launches used to make huge headlines and STS-51L was special. Aboard Challenger was Christie McAuliffe, the first teacher to venture into space. 73 seconds after the launch something went terribly wrong. Horrified viewers both at home and NASA’s space control stations watched the shuttle and the rockets blow apart. The shuttle program was grounded.

Today, there are four shuttles, the newest being Endeavour, which started flying in 1992. The others are Atlantis, Discovery and the original Columbia. The Space shuttle program is not without criticism. Many detractors believe it is an enormous waste of taxpayer money with negligible returns. While such statements can be argued, what is harder to justify is the boondoggle called the International Space Station (ISS).

The ISS is an eternal work in progress. It is a contraption in orbit that consumes money and resources with a vengance. Building the ISS started in 1984 and there is no end in sight. It was projected to cost $8 billion. In 1993, $11 billion later, the Russians were brought in as a key partner, a move that was supposed to save $2 billion. Today the tab has run over $80 billion and is expected to top $100 billion by the time this mess is put to rest.

The current space shuttle mission is carrying a thing called a “truss”, costing $600 million to the space station. According to NASA, the “truss is the first component of a 350-foot long structural backbone for the station”. Supposedly this contraption when attached to the station will allow some vehicles to move around.

Compared to the Space Station, the other NASA missions are cheap, interesting and in many ways quite amazing. Today, Cassini is on its way to Saturn, while Galileo is orbiting Jupiter. The Odyssey is spinning around Mars accompanied by Surveyor, sending back fascinating amounts of data. The Voyager pair is out there, somewhere.

The Voyager-1 has been in space for 25 years and is accompanied a few steps behind by Voyager-2. They were sent up to study Jupiter and Saturn. It was anticipated the crafts would travel far away, but no one really know where and how. Today, they are about twice the distance from the Sun as Pluto and still in touch with NASA. The entire cost of this 25-year old program is estimated to be under $1 billion, a little over the manufacturing cost of the truss for the ISS.

It is not quite clear how the radios and antenna and power supplies put into the tiny Voyager spacecraft is not only functional after 25 years, but reachable while they are 8 billion miles away. But they are. Today’s spacecraft, of course packs much more sophisticated stuff. In fact, sophistication has actually become an intractable problem.

Every space probe has a huge amount of computerized instruments on board. Ground based computers not only control them, but they send back voluminous amounts of data. Images, observations and other data are continuously sent from the spacecraft, and since the communication links from space run at quite a high speed (thanks to modern technology) the amount of data received back at NASA is stupendous. In fact some people claim, that NASA spends most of their resources storing the data and does not get any time to analyze the data. While this is not quite true, processing the mass of data is indeed a significant challenge to the space program.

The space shuttle today is however the most visible of NASA ventures. The four shuttles fly about 7-8 missions a year, with up to seven people on board. The astronauts spend up to two weeks days in space with a heavy workload of experiments, repairs, construction and space walks.

One of the critical flight stages of the shuttle that is often ignored is the landing sequence. The shuttle orbits the Earth between 190 miles to 220 miles above the Earth and traveling at about 18,000 mph. To achieve a return, the shuttle is placed in a tail forward position (the craft points backwards). Then the rocket engines are fired to slow it down, in a procedure called “de-orbit”. As the shuttle slows, it drops. Soon, it is turned around so that the nose is forward, in preparation for re-entry. As the shuttle loses altitude, its speeds up and everything is pre-calculated such that, when at an elevation of 75 miles (400,000ft) it is traveling at 17,300 mph. Then the shuttle hits the atmosphere.

Flying out of space at 17,300 mph into the atmosphere is almost like hitting a brick wall. The friction of the air pulling the shuttle back makes it heat up and become a fireball, surrounded by superheated ionized air. Temperatures on the skin soar to 2000°F (1100°C). Ceramic tiles on the surface of the shuttle attempt to shield and block this fiery nightmare of re-entry. During re-entry and the ionized air severs all radio communications and the blackout lasts 16 minutes. The deceleration is set by the angle of attack to be 33 feet per second squared (or about 1G).

Buffeted by the atmosphere the shuttle slows down to 1,700mph at a height of 16 miles (84,000 ft). At this point, the shuttle is 52 miles from the point of touchdown, and enters the last phase of the landing. From here to touchdown, the shuttle flies like a plane with two important differences.

First, there are no engines. The rocket engine was expended for slowing down, and cannot be used for flying the shuttle. Planes use engines heavily during landing for speed control and descent control. Engines are also extremely important to perform the “go-around” in case of an aborted landing. But for the shuttle, there are no engines, and hence there is no second chance for the landing.

Second, the engineless shuttle may seem like a glider, but it is not. It does not have the long wings of a glider. Its short stubby wings are not good for generating much lift. In size the space shuttle is like a small plane—about the size of a DC-3 “Dakota”. However the DC-3 has a wingspan of 93 feet and weighs 25,000 lbs. The shuttle has a wingspan of only 75 feet, but weighs 240,000lbs (ten times as much!). A small jet lands at about 170 mph, the shuttle has to land at 230 mph.

Hence you can visualize the problem. Hurtling down from 84,000 feet, at 1,700 mph, it has to be slowed down to about 300 mph and then set up for a landing at a runway 52 miles away, with no engines. Instruments do help; they show up as displays with a million dials showing speed, direction, altitude and navigation information. But the actual control is the touch of human hands on the flight control surfaces. Pilots of jet aircraft train over and over again, with an accomplished pilot in the other seat coordinating the moves. How does the pilot of a space shuttle achieve the seemingly impossible landing, always at the first shot? I really have no idea.

Partha Dasgupta is on the faculty of the Computer Science and Engineering Department at Arizona State University in Tempe. His specializations are in the areas of Operating Systems, Cryptography and Networking. His homepage is at http://cactus.eas.asu.edu/partha