All posts by Tom Logsdon

For more than 30 years, Thomas S. Logsdon, M. S., has worked on the Navstar GPS and other related technologies at the Naval Ordinance Laboratory, McDonnell Douglas, Lockheed Martin, Boeing Aerospace, and Rockwell International. His research projects and consulting assignments have included the Transit Navigation Satellites, The Tartar and Talos shipboard missiles, and the Navstar GPS. In addition, he has helped put astronauts on the moon and guide their colleagues on rendezvous missions headed toward the Skylab capsule. Some of his more challenging assignments have centered around constellation coverage studies, GPS performance enhancement, military applications, spacecraft survivability, differential navigation, booster rocket guidance using the GPS signals and shipboard attitude determination. Tom Logsdon has taught short courses and lectured in 31 different countries. He has written and published 40 technical papers and journal articles, a dozen of which have dealt with military and civilian radionavigation techniques. He is also the author of 29 technical books on various engineering and scientific subjects. These include Understanding the Navstar, Orbital Mechanics: Theory and Applications, Mobile Communication Satellites, and The Navstar Global Positioning System

The Bumpy Road to Space

The recent abort, and eventual successful launch, of the Space-X mission to resupply the space station is one of many bumps in the road to commercial space.  One should not expect the road to be smooth, or that replacing a Russian supply system with over a half century and almost 1,000 missions in its heritage will be easy.  While we all hope that the commercial efforts of such companies as Space-X and Orbital Science Corporation will succeed, we also know many problems will arise.

According to Ed Keith, an ATI teacher of rocket and missile design and technology, the NASA commercial space road is a major step in the right direction.  On the other hand, he sees many bumps along that same road.  Historically, American launch vehicles have been developed and operated with large government budgets.  New commercial ventures have an incentive to do the same type of missions at much lower cost.  This means that some short cuts are made, some new risks are accepted, and new ways of doing business are employed.

In Mr. Keith’s three day class on Fundamentals of Rockets and Missiles, the questions of commercial versus government design standards are compared.  The apparent effect is that a commercial rocket DDT&E (Design, Development, Test & Evaluation) effort, like the Space-X Falcon, should cost about one-fifth of what a government DDT&E program costs for a comparable sized rocket.  This cost difference is documented in some cost models or Cost Estimation Relationships (CER).  These same cost models fail to explain why any but commercials should be chosen.  Mr. Keith’s explanation is that the shortcuts have one major impact; lower initial reliability.  Indeed, the first three launch attempts of the Space-X Falcon-1 launch vehicles all failed.  Since then, there have been two successful launches of the Falcon-1 and three successful launches of the much larger Falcon-9.  Commercial space ventures have the opportunity to take calculated risk short cuts that government programs are mandated to avoid, and the business incentive to make wiser trade-offs and choices.

This does not mean that the road to commercial space will be smooth from here on in.  A more realistic expectation is for the road to be bumpy.  Space-X has had five successful launches in a row, but their proven historical reliability is five successes in eight tries, or 62.5% reliability. The best we can say regarding the Falcon-9 rocket is that we can be confident it is at least 75% reliable at this time.  If, or when, a Falcon-9 rocket fails in the future, it should be considered a bump on the way to commercial space, not a failure of this new way of doing business.

Even this latest successful launch cannot be counted as a victory for commercial space until the Dragon Space Capsule successfully docks with the Space Station.  While the launch is the most risky six minutes of the mission, Space-X still must get the craft safely to a docking port with all the cargo intact.  The difficulty and risks of rendezvous and docking of a spacecraft to the Space Station should not be underestimated.

There will always be critics of commercial space who will look for negative occurrences to undermine commercial style ventures.  There is also a high probability that a number of future commercial space missions will include embarrassing failures.  The criteria for success in commercial space should not be whether the road is bumpy with occasional failures.  The success criteria should be whether access to space is better, faster and cheaper using commercial methods and incentives than is practical with the type of government bureaucratic methods and incentives that have dominated the final frontier for the past half century.

Dr. Tom Logsdon teaches Orbital Mechanics and Global Positioning Satellite technology classes for ATI.  His colleague, Edward L Keith, teaches Fundamentals of Rockets and Missiles, Space Mission Analysis and Design and other rocket related classes for ATI. These instructors are available to reporters who need more information. Contact ATI at 410-956-8805.

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Requiem for the Space Shuttle

The shuttle transportation was, by any reasonable standard, one of the most complicated engineering projects in the long history of science and technology.  But, as it was implemented, it never made much economic sense.  In part, this disappointing outcome, came about because its payload was too big and heavy to achieve reliable and cost-effective operation.

Why was the shuttle payload so big and heavy?

The shuttle payload was originally baselined at 65,000 pounds.  It never actually carried that much weight: the heaviest payload it ever flew into space was around 50,000 ponds.  But, as a practical matter, even that lighter payload was much too heavy.  Military users insisted on heavy-life capabilities because they wanted to use the shuttle transportation system to launch their big, heavy spy satellites into space.


In my view, a 15,000-pound payload weight would have been a more practical selection.  With a correspondingly lighter orbiter, those troublesome thermal tiles would have been unnecessary.  And the booster could have been towed (using Kevlar cables) from the shuttle landing strip at Cape Canaveral by 747 airplanes up to a 40,000-foot attitude with a release velocity of about 600 miles per hour.


Unmanned cargo missions using the amazingly inexpensive Russian Soyuz booster – or an American equivalent – could have carried heavy components into low-altitude earth orbits at much more affordable prices.

As Figure 1 indicates, the Russians offered to sell the Americans Soyuz missions with 15,400-pound payloads for $12 million each.  On such a mission, the delivery cost for each pound of payload would have been only $780, or about 1/6th the comparable cost of the American Delta II booster.  In my opinion, we should have bought 1000 Soyuz boosters. Instead, we put severe restrictions on the use for boosting American satellites into space.


In my view we lost a golden opportunity.  But, actually, chemical rockets – Soyuz, Delta II, the shuttle transportation system – are the problem, not the solution.  So what is the alternative?


Satellites Without Rockets

As I have often told my students in my “Launch and Orbital Mechanics” short courses:  “There is nothing wrong with the space program that the elimination of chemical rockets wouldn’t cure.” Chemical rockets are dirty, dangerous, fragile, unreliable, and horribly expensive.


A simple mathematic derivation shows that a typical multistage rocket of modern design wastes about 97-percent of its energy accelerating propellants it’s going to burn later.  If cars were similarly inefficient, few people would want to own one.


Is there a better way to launch payload into space?  In my 4-day short courses on “Launch and Orbital Mechanics”, held at key locations around the country, I list and discuss 30 alternatives to chemical rockets.  These include solar electric propulsion, laser-powered rockets, maglev boosters, nuclear powered rockets, tethered satellites, and skyhooks (space elevators).  These alternatives, implemented in the proper combination, could revolutionize the way future generations conduct large-scale operations and do business in space.


What If the Space Shuttle Engineers Had Designed My Car?

Many times, over the years, I have taught at Vandenberg Air Force Base in California where satellites are launched into near polar orbits.  Vandenberg is 175 miles from my home in Seal Beach, California.  It is one of the few short-course locations I drive to in my car.  Mostly I fly to the various locations where the courses are offered.


A few years ago, I was driving back home from Vandenberg Air Force Base when an interesting question occurred to me:  “What would my car be like if the engineers who designed the space shuttle orbiter had designed it?

When I got back to Seal Beach, I kludged together Figure 2.  Study its contents to see how incredibly inefficient the shuttle transportation system turned out to be. Notice, for example, that only 1 percent of the lift-off weight of the shuttle transportation system is useful payload that ends up being left in space.  If my car had been designed with similar payload-carrying capabilities, it would be able to deliver only one 21-pound briefcase to Vandenberg or any other destination 175 miles away.


Expendable rockets are not much more efficient.  On a typical mission only about 2.5 to 3.0 percent of their lift-off weight is useful payload.  Isn’t it becoming abundantly clear why there’s nothing wrong with the space program that the elimination of chemical rockets wouldn’t cure?”



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Today virtually every large liquid rocket that flies into space takes advantage of the performance-enhancement techniques we pioneered in conjunction with the Apollo moon flights. NASA’s reusable space shuttle, for example, employs modern versions of optimal fuel biasing and postflight trajectory reconstruction. However, more of the critical steps are accomplished automatically by the computer.

Russia’s huge tripropellant rocket, which was designed to burn kerosene-oxygen early in its flight, the switch to hydrogen-oxygen for the last part, yields important performance gains for precisely the same reason the Programmed Mixture Ratio scheme did. In short, the fundamental ideas we pioneered are still providing a rich legacy for today’s mathematicians and rocket scientists most of whom have no idea how it all crystallized more that 40 years ago.

Illustration 1. below summarizes the performance gains and a sampling of the mathematical procedures we used in figuring out how to send 4700 extra pounds of payload to the moon on each of the manned Apollo missions. We achieved these performance gains by using a number of advanced mathematical techniques, nine of which are listed on the chart. No costly hardware changes were necessary. We did it all with pure mathematics!

In those days each pound of payload was estimated to be worth five times its weight in 24-karat gold. As the calculations in the box in the lower right-hand corner of Illustration 1. indicate, the total saving per mission amounted to $280 million, measured in 2009 dollars. And, since we flew nine manned missions from the earth to the moon, the total savings amounted to $2.5 billion in today’s purchasing power!

We achieved these savings by using advanced calculus, partial differential equations, numerical analysis, Newtonian mechanics, probability and statistics, the calculus of variations, non linear least squares hunting procedures, and matrix algebra. These were the same branches of mathematics that had confused us, separately and together, only a few years earlier at Eastern Kentucky University, the University of Kentucky, UCLA, and USC.


Illustration 1. Over a period of two years or so a small team of rocket scientists and mathematics used at least nine branches of advanced mathematics to increase the performance capabilities of the Saturn V moon rocket by more than 4700 pounds of translunar payload. As the calculations in the lower right-hand corner of this figure indicate, the net overall savings associated with the nine manned missions we flew to the moon totaled $2,500,000,000 in today’s purchasing power. These impressive performance gains were achieved with pure mathematical manipulations. No hardware modifications at all were required.

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