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Authors: Robert L. Forward

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The human explorers of Dragon’s Egg used gravitational techniques to move into and survive in a synchronous orbit around the neutron star. The prime mover for all of the gravitational maneuvers near Dragon’s Egg was the large deorbiter mass. Originally a small planetoid about 1000 kilometers across, it had been picked up (along with other asteroidal debris) by the neutron star in its wanderings. The planetoid was condensed by the humans into an ultra-dense mass one kilometer in diameter by injection of magnetic monopoles.

Figure 9
. Dragon Slayer—Side View (Arrows indicate steady component of gravity tides)

There were actually two large condensed asteroids made at the same time. One was used in a close-encounter gravity whip to drop the deorbiter down from its original orbit out in the “asteroid belt” of the neutron star into the desired orbit. This orbit was a highly elliptical one with a perihelion at 406 km and aphelion at 100,000 km, where the human interstellar ship, St. George, moved in a 12.82-minute circular orbit.

Figure 10. Dragon Slayer—Top Deck

The elliptical orbit of the deorbiter mass (called Bright’s Messenger by precontact cheela) had a period of 4.56 minutes or 9.53 greats of turns of the neutron star. It thus took it only 2.28 minutes or 4.77 greats of turns to drop from the safe circular orbit of St. George to the dangerous synchronous orbit at 406 km above Dragon’s Egg.

The gravity field of the neutron star is 400 million gees at the 406 kilometer altitude of Dragon Slayer. However, since the spacecraft was in orbit around the star, most of that 400 million gees was canceled by the fact that it was in a “free-fall” orbit. However, an object is only in free fall at its exact center of mass. When the middle of your body is in a free-fall orbit around a neutron star at 406332 m distance it will feel nothing. But if you are oriented with your feet toward the star, your feet, which are at 406331 m away from the star, are pulled by a gravity force that is 202 gees more than your middle, while your head, at 406333 m distance, is being pulled by a force that is 202 gees less than your middle. If your body is oriented in a direction tangent to the neutron star, your head and feet will feel a 101-gee compression instead of a 202-gee pull. A human cannot survive at a distance of 400 km from a neutron star without some kind of protection from these tidal forces.

Figure 11. Dragon Slayer—Main Deck

Figure 12
. Dragon Slayer—Lower Deck

To protect the humans in Dragon Slayer from these residual gravity tidal forces, six tidal compensator masses were placed in a 200-meter radius ring about the science capsule and arranged so that the plane of
the six masses was always at right angles to the direction to the neutron star. The compensator masses were made from asteroids about 250 km in diameter that were condensed to 100 m in diameter.

In the center of that ring of ultra-dense spheres, the masses are attempting to pull anything at the center out toward them. At the exact center of the ring all the forces cancel. However, if your head or feet are in the plane of the ring, since they are about one meter away from the exact center of the ring, they will be pulled with a force of 101 gees. If you try to orient your body to point along the axis of the ring, your head and feet will be compressed with a force of 202 gees. If made dense enough and placed at the right distances, the six compensator masses will cancel the neutron star tidal forces over a seven-meter diameter spherical region. (See
Figure 9
which shows the residual tidal forces around Dragon Slayer).

In operation, the six compensators rotate about Dragon Slayer as it orbits the star at 5.018 rps. The individual orbits of the compensator masses are almost in a natural gravitational orbit, but require that the masses change speed slightly each half orbit to maintain the circular formation. This is accomplished by magnetic interactions between the magnetically charged compensators, assisted by trimming maneuvers carried out by robotic herder probes using monopole-catalyzed fusion rockets.


The only significant personal contact between the cheela and the humans occurred for a period of 1.2 seconds on 20 June 2050 between Clear-Thinker of the cheela and Pierre Carnot Niven of the humans. This was a short interval during the occasion of a ten-second visit by a cheela expedition to examine the human spacecraft and the humans inside.

The cheela had to go to great lengths to protect themselves and the humans from the effects of gravity. The cheela would explode if their bodies were not kept under sufficient gravity to keep their matter in a degenerate state, and the gravitational fields that were comfortable to the cheela were destructive to human flesh.

The main cheela spacecraft was a crystal shell 4 cm in diameter. With its large number of docking pits for the smaller instrumental shells and individual flyers, it had the size and appearance of a golf ball. The main ship had a black hole of 11 billion tons mass at its center that kept the surface of the cheela ship at a gravitational level of 0.2 million gees. Although nowhere near the gravitational field strength on their neutron star home, the gravity was enough to keep the cheela from exploding. The gravity field on the humans inside the Dragon Slayer at a distance of 15 m away from the main cheela spacecraft was a reasonable 1/3 gee.

Clear-Thinker used a smaller individual flitter with a much smaller black hole of only 0.22 billion tons mass. This flitter was only 5 mm in diameter (just slightly larger than a cheela body) and the surface gravity again was sufficient to keep Clear-Thinker’s body from exploding. This smaller personal flitter could come within 70 cm of a human, so that the human eyes could actually see some detail of the glowing-hot cheela body. (For a well-written description of this unique scene, see Reference 4.) Even at that, the gravitational field on the nose of the human, P. C. Niven, was over three gees.

We do not know the propulsion technique used by the cheela to lift their spacecraft off the surface of the neutron star (the escape velocity of Dragon’s Egg is 1/4 the speed of light). We also do not know the propulsion technique that they use in space. The human
observers during the Visit, P. C. Niven and A. S. Drake, saw no evidence of any rocket-type mechanism in the cheela spacecraft. From their conversations with the cheela communicators, they suspect that the cheela used some sort of antigravity catapult to get off the star, and some form of inertia drive in space. Our only clues are some old speculative papers (see References 5 and 6) based on the now-suspect Einstein theory of gravity.

At the time of this writing (2063), the knowledge of the antigravity and other space drives, including a faster-than-light drive, remains locked in the encrypted sections of the HoloMem crystals containing the knowledge of the cheela after they surpassed the human race in development. Present estimates are that we will be able to duplicate the cheela antigravity catapult (and decode that section of the HoloMem) in another 10 years. We have only a few clues on the inertia drive. Scientists estimate that it will take us at least two more decades before we learn enough to find the code to that section.


1. V. Sawlinski et al., “A nearby short period pulsar,”
Astrophysical Journal, 561
, 268 (2020)

2. S-Y Wang, “The Egg of the Dragon—Sol’s Nearest Neighbor,”
Astro. Sinica, 83
, 1789 (2020)

3. F. D. Drake, “Life on a Neutron Star,”
, Vol. 1, No. 5, 5 (Dec. 1973)

4. P. C. Niven,
My Visit with Our Nucleonic Friends
, Ballantine Interplanetary, New York, Earth and Washington, Mars (2053)

5. R. L. Forward, “Guidelines to antigravity,”
Am. J. Physics, 31
, 166 (1963)

6. R. L. Forward, “Far Out Physics,”
Analog Science Fiction/Science Fact
, Vol. XCV, No. 8, 147 (August 1975)

BOOK: Dragon's Egg
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