The physics of Thunderbird 5

Theo de Klerk

In recent years there have been many publications and articles attempting to explain the hypothetical science (minus the fiction) of numerous TV, film and comic book favourites. Perhaps these studies are not every fan's cup of tea — as there is always the danger of taking things a little too seriously, not to mention the risk of demystifying the magic of the fantasy. However these technical manuals can offer a fun insight into the 'what ifs' lurking behind all good science fiction and help to explore what the original writers had in mind whilst creating our TV favourites.

As a physicist myself, a book that I would love to have would be one which discusses the science of Thunderbirds. To read of how the craft and hardware of International Rescue could function in the real world, and to gain a feel for what is realistically possible and what is not from the Andersons' future 21st Century world.

So in the end I did the research myself. Some people ask if knowing that it is all impossible doesn't spoil the illusion. For me it doesn't. As a kid I felt shortchanged if the cheaply inserted stock footage of the Thunderbird launches was not included. It is part of the magic. Magic that requires Thunderbird 2 to launch only from its ramp once the palm trees are (unnecessarily?} swung aside. That this entire launch is more than a little superfluous and inefficient taken from a realistic point of view does not deter from its sheer visual imaginative power.

Like many fans. when I watch Thunderbirds, I enter a make believe world and put reality aside, it's a tribute to the original creative team that this makebelieve world still retains a lot of convincing realism, so the question begs itself: just how realistic is it, and how much is really impossible, but still highly enjoyable — after all, Superman cannot physically fly either.

For this first article, I begin my study in the depths of outer space and look into the physics of International Rescue's space monitoring satellite, Thunderbird 5.

Shape and construction

Thunderbird 5 side
Side elevation
Thunderbird 5 plan
Thunderbird 5 underside
Reverse plan

Updated technical specifications

Thunderbird 5 is a space satellite that operates in an almost perfect vacuum, meaning there are no atoms that can be pushed aside to carry sound or offer any air resistance. The shape of TB5 therefore can be completely determined by functionality, unlike the Earthbound Thunderbird craft that are aerodynamiadty designed to plough their way through the atmosphere or ocean water.

The space station is too large in size and heavy in weight to be brought into orbit with a single rocket. Just like the real life International Space Station (ISS), TB5 must have been assembled in space from prefabricated components brought into space individually — most likely through Jeff's 'Tracy Construction and Aerospace Corporation' as envisaged by Alan Fennell in his long-running 90s comic The Complete Thunderbirds Story.

Safety for human occupation

The vacuum of space and the required atmospheric environment inside the living quarters pose severe conditions on the bulkheads of the habitable interiors of TBS. The living quarters must be air-sealed and able to withstand the pressure difference between vacuum outside and living quarters inside.

The walls themselves must also be good insulators to avoid the warmth of room temperature (293°k, 20°c inside the living quarters radiating away into space leaving Thunderbird 5 at almost absolute zero temperature (0°k -273°c).

Like any vehicle in a hazardous environment, TB5 must be divided into compartments to spread the risk of damage — especially the living quarters. Each section should be easily sealed off to minimise any disaster in case one part of the satellite is compromised and to maximize the survival chances of its occupants.


geostationary orbit

It is described that TB5 is in a geostationary orbit (also known as a (Arthur C.) 'Clarke orbit'), meaning that it would 'hang' above Tracy Island and rotate with the same angular speed as Earth itself, with one rotation per day.

From a real-life science perspective, however, there are various reasons why this would be problematic. The first reason is based on the fact that there is a unique relation between the radius of the orbit (distance from the centre of the Earth) and its orbital period. In any such orbit a satellite can move without spending energy so it doesn't need rockets and fuel to stay in that orbit. Just like the Moon doesn't require any energy to circle around the Earth. In any other orbit fuel would be needed to keep it in that orbit, which would quickly limit the life-span of a satellite.

A geostationary orbit is known as a Kepler orbit with an orbital period of one day. This automatically fixes its orbital radius. Any lower Kepler orbit is completed in less than a day and any higher one takes longer. Other orbits are possible only at the expense of fuel usage. Geostationary also implies the orbit is above the equator and not circling the poles. Only then can a satellite hang still above one spot on Earth.

Tracy Island's timezone

Based upon dialogue and various promotional materials, it is safe to assume that Tracy Island is not on the equator. There is a five hour difference with Lady Penelope's stately home in England (as detailed by Jeff Tracy in Thunderblrds Are GO!) which positions the island in the GMT-5 time zone – most likely somewhere in the Pacific south of Peru – which would be quite near the coast of the continent. TB5 cannot therefore realistically be in geostationary orbit.

The second reason is that despite what the many Thunderblrds magazines, comics and books suggest, today more than 8,000 commercial communication satellites are found in geostationary orbits — not a place you want to be if you try to remain undetected. In the 1960s when Thunderbirds was conceived the geostationary orbit was almost empty.

Earth's van Allen belts

Another problem for satellites are the two Van Allen belts that surround the Earth. Caused by the magnetic field of our planet, the Van Alien belts (discovered in 1958 by professor Van Allen) look like two concentric doughnuts which surround the planet. Charged and radioactive particles from the Sun are caught within the belt, preventing them from doing harm to life on Earth. No satellite owner would place his satellite within these belts: the particles would damage the satellite and any life aboard is also trreatened if exposed to the radiation for a prolonged penod of time. To avoid these dangers of detection and particle penetration it seems safe to assume that TB5 is positioned beyond the second Van Allen belt, possibly at a height of 15 Earth radii {or 95,500km).

As detailed in the 1966 Thunderbirds Annual, the precise orbital position of TB5 is maintained through the star-fix sensors housed within transparent domes seen on top of TB5. Fine tuning of TB5s orbit requires a retrorocket system (as detailed in the original cutaway as located along the circumference of TB5) enabling orbital adjustments in all directions. This would naturally consume some fuel which we can assume would be replenished when Thunderbird 3 visits on its regular monthly relief rotation.

Additional satellites

Thunderbird 5's footprint

Whatever orbit TBS occupies, it can only see part of the Earth: its footprint. Additional satellites would be needed to have communication coverage of the entire Earth. Given the footprint of TB5 when at the proposed 95,500km radius orbit, a minimum of three satellites are needed. When these satellites remain in the plane of the equator they still see little of the higher geographical altitudes (50° and higher) or the poles.

Spreading these satellites around the Earth (still in a Kepler orbit) and adding a fourth satellite resolves this problem. When all satellites are positioned at equal distances from each other, they form a pyramid with three sides and triangular base (known as a tetrahedron with equal sides). Each of the satellites can directly see the other three: they are all in direct lines of sight and hence of communication. And each sees more than a quarter of the Earth — from all angles. Together they could provide complete communication cover for the entire Earth.

Thunderbird 5's booster satellites

In this configuration with three booster satellites, TB5 serves as the 'main' satellite. At any one time, one of the four satellites has Tracy Island in its footprint and will function as relay station for TB5 to communicate with Tracy Island. The distance between all satellites is the same, as is their height above Earth.

With TB5 (and the satellites) being in orbit at 95,500km, the distance between TB5 and its satellites is about 153,000km. Communication between them takes half a second.

Assuming some computing intelligence is in place within these booster satellites, they would operate much like TBS tself, filtering distress calls and ignoring anything else they receive before sending that information on to John or Alan in TB5. Perhaps these three booster satellites could have been named Thunderbird 6, 7 and 8? The Thunderbird moniker is arguably more deserved than the biplane nicknamed Thunderbird 6 in the second movie!

Communication with Tracy Island would take another .3 seconds. A total delay of anything between .5 and .8 seconds. This would be noticeable in a dialogue with 2 x .8s delay between speaking and receiving a response. Apparently it has become second nature to the Tracy family.

At this point I am tempted to venture (in the spirit of fan conjecture) that initially at the end of a line of speech in communication to TB5 the Tracy family coined the phrase 'Finished Answering Broadcast' or 'F.A.B.' for short. Perhaps the phrase stuck as an inside toke with the Tracy boys to sign off all their com chatter?


Whilst it is in a Kepler orbit, TB5 is in constant free fail to Earth, meaning that anyone inside TB5 would be weightless. Persons or objects have their mass (the sum total of all molecules that make up a person or object) and they would feel the gravitational puli of Earth. But since everything is falling at the same rate in the same direction, no one would weigh anything as there is nothing that pushes against them to give them weight.

Like most other space based film and TV science fiction, there is no real world science explanation as to how the occupants of TB5 are able to stand on their feet, and navigate the interiors of the space station. The Tracy brothers would float around the interiors unless some form of magnetic footware held them down to the deck… However. this would not explain why the other objects such as books, pens, flowers and other contents of TB5 are not floating around! Naturally, weightless situations are difficult to film on Earth, even for a talented bunch of film makers based in Slough 50 years ago.

According to 2012 Haynes Thunderbirds Manual, TB5 is fitted with 'Previn Coil Artificial Gravity Generators'. This is a chapter in physics that has yet to be written, although apparently also in use in Skyship One.

Communication techniques

It would make sense for this hypothetical fleet of Thunderbird satellites to transmit an encoded signal only when something needs to be transmitted, probably with the use of a directed (laser) beam via non-standard frequencies to reduce the risk of interception, This is efficient and reduces the chance of being detected during transmission. Communicating with Earth is more detection-prone. To intercept distress calls, each of the Thunderbird satellites would require a main monitor antenna on a long pylon underneath each satellite. This antenna is always pointed to Earth and receives the distress calls made at ordinary radio frequencies. Because the satellites are in a high orbit, sensitive equipment is needed to intercept these faint distress calls from Earth.

Communication with Tracy Island can be carried out using focused radio beams which need to be of ordinary radio wavelengths as Earth's atmosphere absorbs most other types of wavelengths. A satellite transmission is possible using the 8 parabolic antennas, These antennas are mounted underneath TB5 (and each of the booster satellites), and would explain the large protruding structures seen on the underside of TB5 in the series.


Space is a dangerous place with the potential of meteorites and other moving debris. As detailed in the 1966 annual, TB5 has a constant monitoring system that detects the smallest of objects that enter a sphere of 100km around the satellite. It can be assumed that very large objects that are a risk to TB5 cannot be destroyed or deflected without attracting attention from other satellites and monitors of space. Perhaps it would make sense to maintain the secretive nature of the station with the use of selective retro- rockets to temporarily reposition TB5's orbit, allowing the oncoming objects to fly by without causing harm.

Small objects could be diverted by small intense laser beams, perhaps something similar to the established International Rescue beam technology much like Thunderbird 3 uses to remotely fire the retro rockets of the distant Sun Probe. An intense short laser blast could produce a sufficient amount of radiation pressure on the object to divert it from its course, working much the same way as a snooker ball transfers some of its momentum to other balls, changing their direction, in this case to avoid a collision with TB5.

Be seeing you… or not

Even in space an oblect is only invisible when it does not reflect any light of any frequency. No reflection means TB5 would need to be completely black externally thus absorbing all light thrown at it. Obviously this is not the case with TB5's complex exterior design.

Essentially, there is no physical way that TB5 could remain undetected. A solution which is hinted at in the series suggests that TB5, as well as its hypothetical family of booster satellites, have been registered with the World Space Administration (as seen in The Impostors, and further mentioned in Ricochet) as being communication satellites owned by Jeff's Tracy Construction and Aerospacs Corporation, naturally under false names. This way no one would suspect anything out of the ordinary when spotting the satellites along their established orbital paths.

This of course would not prevent detection but it would reduce the number of sightings significantly when it is seen the registration will defuse any suspicion and the satellites are simply hidden in plain sight. Come to think of it… it might not be the best of ideas to advertise the name of the satellite in bold lettering on the outside!

Power generation

Naturally, TB5 requires power to keep its distress signal detection systems running, not to mention providing habitable living conditions and power to fire its retro-rockets when needed. Where does the power come from?

'Atomic power' is often mentioned in the Anderson series as a source of energy, no doubt because it sounded effectively futuristic to the viewers in the 1960s. However, by today's standards it is old hat and also incorrect. Fossil fuel provides atomic power — this doesn't sound like a plausible power source used by TB5. Solar energy is also not likely as solar panels would only work effectively when sunlight is received and when TB5 is not in the shadow of the Earth or Moon. Also, the reflection from the solar panels would be a bit of a detection risk as many satellites with solar panels can be easily spotted from the Earth.

It makes sense for nuclear fusion power to be the way to go. Efficient and requiring little fuel, it is likely to assume that the fusion engine of TB5 is a variation of the Tokamak fusion reactor developed in Russia in the 20th century. Interestingly, Tokamak stands for toroidal chamber with magnetic coils — a torus shaped chamber surroundec by magnets… sounding not too dissimilar to that large copper coloured ring around the edge of TB5! Could Derek Meddings have known this when originally doodling the design? This ring would be used to speed up hydrogen nuclei by letting them run in circles until they can collide to form helium nuclei, releasing enormous amounts of energy in the process. With 1.5kg of fuel TB5 could generate as much enerqy as New York City consumes in a vear.

With the knowledge gained, the initial cutaway released on Thunderbird 5 needs some updating (text in bold italic font) whilst other parts seem remarkably correct upon first release.

Thunderbird 5 cutaway drawing Thunderbird 5 lounge
Move the pointer over the numbers in the drawing
to access the legend
Tap a circle to access the legend
tap anywhere else to cancel
Twin gate space scanners for detecting large and medium sized meteors and debris before it hits Thunderbird 5
Special frequency antennae for direct communication with the base laser-bundle antenna for communication with the three other communication satellites TB6, 7 and 8
Space signalling laser beamintense Laser beam to divert medium and small meteors off course before the hit Thunderbird 5
Lock-on star-fix sensors coupled to computer controlled jets which maintain the satellite in correct position to keep Thunderbird 5 in precise orbit such that all Thunderbirds 5, 6, 7 and 8 remain in fixed position relative to each other
Astrodome housing of the telescope; this high resolution instrument can be used manually or coupled to a TV screen in the monitor room
Duplicate monitor room; in case of a major fault the damaged room is vacated and the operator walks through to the duplicate – this also means that Thunderbird 5 is never out of commission during overhaul
Lift tube to other floors
Airlock; these are strategically sited throughout the satellite as a precaution against air leakage
Main monitor room
Movable screens to cover the window against sun glare
Stores and replacement parts
Amplifier housing for twin gate scanner signals to be fed to meteor detecting systems
Lift tube, emergency ladder and catwalk to Thunderbird 3 dock
Sleeping accomodation with foldaway bunks
Double walls filled with coagulant compound to seal micro meteor punctures and stop charged particles from solar and stellar winds; also houses liquid helium carrying pipes to stop space neutrons from damaging the satellite and its occupants
Cables and plasma pump supplying cables and fuel supply pipes for the retro-rockets that are used to keep Thunderbird 5 in calculated orbit; functioning ruled by information from the lock-on star-fix sensors above as well as the docking guiding system when Thunderbird 3 docks
Plasma core localised field meteor deflector modified Tokamak plasma ring; the coils produce magnetic fields that keep the deuterium and tritium nuclear plasma in the center of the ring before fusing to helium and releasing energy for use by Thunderbird 5 equipment
Field localiser magnetic pole unit energy exchange baffle; water turns to steam when transfering the nuclear energy produced in the ring into Thunderbird 5 turbines for convertion into electricity
Main generating room using atomic batteries and piles occupying most of the floor; includes the turbines to convert steam energy into electrical energy to supply the equipment used in Thunderbird 5
Electromagnetic baffle – one of a ring of anti-radar devices set in the base used to prevent accidental discovery one of 8 parabolic antennas focused on Tracy Island when Thunderbird 5 is in line of sight; transmissions are scrambled and bundled in focused beams, limiting detection of the space station; the antennas are only visible and used while Tracy Island is visible, afterwards they are withdrawn inside the station hull to protect them from micro meteors; when Thunderbird 5 is not in line of sight, communication is done via relay by one of the relay satellites' parabolic antennas; communication with the other satellite occurs via the laser-bundled antenna above
Docking ramp for Thunderbird 3
Fuel tanks for 'topping up' Thunderbird 3 deuterium fuel supply tanks for the nuclear power generators in the ring around Thunderbird 5; they can be ejected in case of emergency
Docking port precise guiding system used by Thunderbird 3’s docking system stored in its white sealing ring; combined with the retro-rockets to keep Thunderbird 5 in precise orbit and not pushed away by Thunderbird 3’s rockets
Inspection platform
Heat dispersal unit
Long pylon holds main antenna clear of distortion caused by anti-meteor device to receive emergency calls on any radio wavelength; always pointed towards Earth
Solitary duty over long periods can be a great strain – in order that the monitors' efficiency shall be unimpaired, great attention has been paid to providing more than adequate rest facilities; here we show a portion of the lounge
TV screen which can also be used in conjunction with a film library
Direct communication screen and speaker relaying messages from Tracy Island functioning through the parabolic or laser-bundle antennas above
Warning light and speaker linked to a special computer which has been programmed to select all messages containing words such as 'Help', 'Emergency', &c. in all of the world's languages, and relay them to positions all over the satellite thus alerting the operator (the panel in the sleeping quarters contains a warning alarm signal as well as a light)
Hand microphone linked to broadcasting system
Air conditioning and life support system
Door to sleeping quarters
Pot plant growing in nutrient solution, one of John's hobbies
Part of the immense library of books, tapes and film; not surprisingly, John spends a lot of his duty time studying languages all are stored in digital format and can be accessed via many gadgets but here are some classical, physical and touchable items.
Tape selector for concealed record player
Not only a coffee table but at the touch of a button producing a variety of refreshing drinks from beneath via the rising plate on the top but also food printer to create any dish stored in the computer system of Thunderbird 5
Spacecraft System Engineering, 3rd Edition, Peter Fortescue (Editor), John Wiley, 2005
Introduction to Flight 5th Edition, John D. Anderson Jr, McGraw Hill, 2005
Physics 7th Ed. – Cutnell & Johnson, Wiley & Son, 2007
Inventions from outer space – David Baker, Marshall Editions, 2000
The world of Star Trek – Lawrence Krauss, Collins Publishers, 1995
Beyond Star Trek – Lawrence Krauss, Basic Books, 1997
Gold medal physics – John Erik Goff, John Hopkins University Press, 2010
Thunderbirds – Haynes’ Agents’ Technical Manual, Graham Bleathman & Sam Denham, Haynes Publishing 2012
Thunderbirds – Code Oranje – Albert Heijn, 1966
Thunderbirds Annual 1966, City Magazines, 1966
Thunderbirds Are Go! – J.C. Coxon, J.F. Barker and T.M. Conlon, Journal of Physics Special Topics, 2011
text ©2014 Theo de Klerk
article originally appeared in fab #78