APOD: Trail of the Returner (2020 Dec 31)

[APOD Robot]

Trail of the Returner

Explanation: Familiar stars of a northern winter's night shine in this night skyview, taken near Zhangye, Gansu, China and the border with Inner Mongolia. During the early hours of December 17 Orion is near center in the single exposure that captures a fireball streaking across the sky, almost as bright as yellowish Mars shining on the right. Splitting Gemini's twin bright stars Castor and Pollux near the top of the frame, the fireball's trail and timing are consistent with the second skipping atmospheric entry of the Chang'e 5 mission's returner capsule. The returner capsule was successfully recovered after landing in Inner Mongolia, planet Earth with about 2 kilograms of lunar material on board. The lunar sample is thought to contain relatively young material collected near the Mons Rumker region of the Moon's Oceanus Procellarum. Launched on November 23 UT, China's Chang'e 5 mission is the first lunar sample return mission since the Soviet Union’s Luna 24 mission in 1976.

<< Previous APOD

This Day in APOD

Next APOD >>

[RocketRon]

Are there any photos yet of the rock and material brought back ?

Be interesting sometime to see a detailed discussion of the mathematics and calculations involved in firing off a rocket to the moon,
getting it into orbit, getting it onto the surface, getting it back into orbit, firing it towards Earth, getting it to skip off the atmosphere
and getting it onto the ground close to X marks the spot.

How do you KNOW the nose is pointing in the right direction.
How do you KNOW how long the rocket burn needs to be.
etc etc.

I know a lot of this is previous experience (witness Mr Musks' Tesla going nowhere near Mars on the 1st attempt !)
(and Boeing not quite getting to the ISS) but quite how do you do 3 dimensional astro navigation for beginners ?
Answers on the back of a postcard, if its not classified ?
Or some suitable discussion somewhere...

[De58te]

@ Rocket Ron. My guess is that if Russia could do it in 1976 with Luna 24, that the Chinese scientists then went over to Russia to study the Russian's electronic schematics of Luna 24, and then the Chinese had 44 years to improve on the computing power and programing.

[orin stepanek]

impressive sample gathering by the Chinees!

Nice photo!

[heehaw]

are consistent with the second skipping atmospheric entry of the Chang'e 5 mission's returner capsule
So is that what it was? I am on tenterhooks!

[johnnydeep]

are consistent with the second skipping atmospheric entry of the Chang'e 5 mission's returner capsule
So is that what it was? I am on tenterhooks!

From https://www.planetary.org/space-missions/change-5 :

Vehicles reentering Earth’s atmosphere from the Moon travel much faster than those returning from low-Earth orbit: about 11 kilometers per second versus 8 kilometers per second. Whereas human-rated vehicles like NASA’s Apollo capsule relied solely on strong heat-shielding, Chang’e-5 performed a “skip reentry,” bouncing off the atmosphere once to slow down before plummeting to a landing in Inner Mongolia. The landing site was the same used for returning crewed Shenzhou spacecraft.

After dropping off its Moon samples at Earth, Chang'e-5 left for one of several locations where Earth and the Sun’s gravity balance in a way that spacecraft can orbit the locations for long periods of time. Chang’e-5 appears to be headed to one optimal for solar observations, and may later move to another to search for near-Earth asteroids.

So, I interpret this to mean that the return capsule hit the upper atmosphere, bounded off, then re-entered at a slower speed to complete its descent. But I'm not clear on how long all that took. Only minutes, tens of minutes, an hour or two?

[neufer]

Be interesting sometime to see a detailed discussion of the mathematics and calculations involved in firing off a rocket to the moon, getting it into orbit, getting it onto the surface, getting it back into orbit, firing it towards Earth, getting it to skip off the atmosphere and getting it onto the ground close to X marks the spot.

How do you KNOW the nose is pointing in the right direction.
How do you KNOW how long the rocket burn needs to be. etc etc.

How do you KNOW how long the rocket burn needs to be

• Force x time = momentum change.

How do you KNOW the nose is pointing in the right direction

• Da Nose knows:

<<A gyrocompass is a type of non-magnetic compass which is based on a fast-spinning disc and the rotation of the Earth (or another planetary body if used elsewhere in the universe) to find geographical direction automatically. The use of a gyrocompass is one of the seven fundamental ways to determine the heading of a vehicle. Before the success of the gyrocompass, several attempts had been made in Europe to use a gyroscope instead. By 1880, William Thomson (Lord Kelvin) tried to propose a gyrostat (tope) to the British Navy. In 1889, Arthur Krebs adapted an electric motor to the Dumoulin-Froment marine gyroscope, for the French Navy. That gave the Gymnote submarine the ability to keep a straight line while underwater for several hours, and it allowed her to force a naval block in 1890. The V-1 flying "buzz" bomb used a gyrocompass based autopilot>>

<<Apollo 8 was the first crewed spacecraft to leave low Earth orbit, and also the first human spaceflight to reach another astronomical object, namely the Moon, which the crew orbited without landing, and then departed safely back to Earth. Jim Lovell's main job as Command Module Pilot was as navigator. Although Mission Control normally performed all the actual navigation calculations, it was necessary to have a crew member adept at navigation so that the crew could return to Earth in case communication with Mission Control was lost. Lovell navigated by star sightings using a sextant built into the spacecraft, measuring the angle between a star and the Earth's (or the Moon's) horizon. This task was made difficult by a large cloud of debris around the spacecraft, which made it hard to distinguish the stars.>>

1919: Ukrainian engineer Yuri Kondratyuk first proposed LOR

---

1961: John Houbolt explains Lunar orbit rendezvous

---

<<Lunar orbit rendezvous (LOR) is a key concept for efficiently landing humans on the Moon and returning them to Earth. It was utilized for the Apollo program missions in the 1960s and 1970s. In a LOR mission, a main spacecraft and a smaller lunar lander travel to lunar orbit. The lunar lander then independently descends to the surface of the Moon, while the main spacecraft remains in lunar orbit. After completion of the mission there, the lander returns to lunar orbit to rendezvous and re-dock with the main spacecraft, then is discarded after transfer of crew and payload. Only the main spacecraft returns to Earth. Lunar orbit rendezvous was first known to be proposed in 1919 by Ukrainian Soviet engineer Yuri Kondratyuk, as the most economical way of sending a human on a round-trip journey to the Moon.

Dr. John Houbolt would not let the advantages of LOR be ignored. As a member of Lunar Mission Steering Group, Houbolt had been studying various technical aspects of space rendezvous since 1959 and was convinced, like several others at Langley Research Center, that LOR was not only the most feasible way to make it to the Moon before the decade was out, it was the only way. He had reported his findings to NASA on various occasions but felt strongly that the internal task forces (to which he made presentations) were following arbitrarily established "ground rules." According to Houbolt, these ground rules were constraining NASA's thinking about the lunar mission—and causing LOR to be ruled out before it was fairly considered.

In November 1961, Houbolt took the bold step of skipping proper channels and writing a nine-page private letter directly to associate administrator Robert C. Seamans. "Somewhat as a voice in the wilderness," Houbolt protested LOR's exclusion. "Do we want to go to the Moon or not?" the Langley engineer asked. "Why is Nova, with its ponderous size simply just accepted, and why is a much less grandiose scheme involving rendezvous ostracized or put on the defensive? I fully realize that contacting you in this manner is somewhat unorthodox," Houbolt admitted, "but the issues at stake are crucial enough to us all that an unusual course is warranted."

It took two weeks for Seamans to reply to Houbolt's letter. He assured Houbolt that NASA would in the future be paying more attention to LOR than it had up to this time. In the following months, NASA did just that, and to the surprise of many both inside and outside the agency, the dark horse candidate, LOR, quickly became the front runner. Several factors decided the issue in its favor. First, there was growing disenchantment with the idea of direct ascent due to the time and money it was going to take to develop a 15 m diameter Nova rocket, compared to the 10 m diameter Saturn V. Second, there was increasing technical apprehension over how the relatively large spacecraft demanded by Earth-orbit rendezvous would be able to maneuver to a soft landing on the Moon.>>

[johnnydeep]

Are there any photos yet of the rock and material brought back ?

Be interesting sometime to see a detailed discussion of the mathematics and calculations involved in firing off a rocket to the moon,
getting it into orbit, getting it onto the surface, getting it back into orbit, firing it towards Earth, getting it to skip off the atmosphere
and getting it onto the ground close to X marks the spot.

How do you KNOW the nose is pointing in the right direction.
How do you KNOW how long the rocket burn needs to be.
etc etc.

I know a lot of this is previous experience (witness Mr Musks' Tesla going nowhere near Mars on the 1st attempt !)
(and Boeing not quite getting to the ISS) but quite how do you do 3 dimensional astro navigation for beginners ?
Answers on the back of a postcard, if its not classified ?
Or some suitable discussion somewhere...

It's all math, math and more math. An intimate familiarity with physics helps too of course. This page seems like a good start - http://www.braeunig.us/space/orbmech.htm :

Orbital mechanics, also called flight mechanics, is the study of the motions of artificial satellites and space vehicles moving under the influence of forces such as gravity, atmospheric drag, thrust, etc. Orbital mechanics is a modern offshoot of celestial mechanics which is the study of the motions of natural celestial bodies such as the moon and planets. The root of orbital mechanics can be traced back to the 17th century when mathematician Isaac Newton (1642-1727) put forward his laws of motion and formulated his law of universal gravitation. The engineering applications of orbital mechanics include ascent trajectories, reentry and landing, rendezvous computations, and lunar and interplanetary trajectories.

There's much more at the link.

[neufer]

are consistent with the second skipping atmospheric entry of the Chang'e 5 mission's returner capsule.

So is that what it was? I am on tenterhooks!

Tenter hook in an 1822 trade catalogue, published by H. Barns & Sons, of Birmingham, England

---

<<Tenterhooks or tenter hooks are hooked nails in a device called a tenter. Tenters were wooden frames which were used as far back as the 14th century in the process of making woolen cloth. By the mid-18th century, the phrase on tenterhooks came to mean being in a state of tension, uneasiness, anxiety, or suspense, i.e., figuratively stretched like the cloth on the tenter. John Ford's 1633 play Broken Heart contains the lines: "There is no faith in woman. Passion, O, be contain'd! My very heart-strings Are on the tenters." In 1690 the periodical The General History of Europe used the term in the modern sense: "The mischief is, they will not meet again these two years, so that all business must hang upon the tenterhooks till then.">>

Vehicles reentering Earth’s atmosphere from the Moon travel much faster than those returning from low-Earth orbit: about 11 kilometers per second versus 8 kilometers per second. Whereas human-rated vehicles like NASA’s Apollo capsule relied solely on strong heat-shielding, Chang’e-5 performed a “skip reentry,” bouncing off the atmosphere once to slow down before plummeting to a landing in Inner Mongolia. The landing site was the same used for returning crewed Shenzhou spacecraft.

After dropping off its Moon samples at Earth, Chang'e-5 left for one of several locations where Earth and the Sun’s gravity balance in a way that spacecraft can orbit the locations for long periods of time. Chang’e-5 appears to be headed to one optimal for solar observations, and may later move to another to search for near-Earth asteroids.

So, I interpret this to mean that the return capsule hit the upper atmosphere, bounded off, then re-entered at a slower speed to complete its descent. But I'm not clear on how long all that took. Only minutes, tens of minutes, an hour or two?

• Tens of minutes to orbit a fraction of Earth's 25,000 mile circumference at ~25,000 mph.

Phases of a skip reentry

---

<<Boost-glide trajectories are a class of spacecraft guidance and reentry trajectories that extend the range of suborbital spaceplanes and reentry vehicles by employing aerodynamic lift in the high upper atmosphere. In most examples, boost-glide roughly doubles the range over the purely ballistic trajectory. In others, a series of skips allows range to be further extended, and leads to the alternate terms skip-glide and skip reentry.

The concept was first seriously studied as a way to extend the range of ballistic missiles, but was not used operationally in this form as conventional missiles with extended range were introduced. The underlying aerodynamic concepts have been used to produce maneuverable reentry vehicles, or MARV, to increase the accuracy of some missiles like the Pershing II or to avoid interception as in the case of the Avangard. More recently, the range-extension has been used as a way to allow flights at lower altitudes, helping avoid radar detection for a longer time compared to a higher ballistic path.

The concept has also been used to extend the reentry time for vehicles returning to Earth from the Moon, which would otherwise have to shed a large amount of velocity in a short time and thereby suffer very high heating rates. The Apollo Command Module used what is essentially a one-skip reentry (or partial skip), as did the Soviet Zond and Chinese Chang'e 5-T1. More complex multi-skip reentry is proposed for newer vehicles like the Orion spacecraft.>>

[heehaw]

It clearly ain't easy, gadding about in our solar system. Better to stay home and watch TV. Maybe.

[Ann]

Trail of the Returner. Image Credit & Copyright: Zhuoxiao Wang.

---

The Winter Hexagon. Photo: Jimmy Westlake.

---

Great thread, and I must particularly thank neufer. What you wrote was beyond me, but the picture of the "skip reentry" was fantastic to me.

What I should have said last year is that it is a great APOD. Just seeing any long meteor streak split Gemini the twins, so that for a moment they are not Siamese twins any more, is remarkable. But here we have one long lonely streak splitting the entire Winter Hexagon, and that's downright amazing.

Not only that, but the streak isn't just any old meteor, not even any old ISS trail, but the path of Chang'e 5 mission's returner capsule, bringing lunar material back to Earth.

Wowzers!

A few words on Jimmy Westlake's great annotated picture of the Winter Hexagon. If it disappears, check it out at https://cdn.steamboatpilot.com/wp-conte ... 40x831.jpg.

The APOD is not oriented in the same way, but you should be able to make out that Chang'e 5 mission's returner capsule enters the Winter Hexagon by splitting Gemini the Twins (Pollux and Castor), and it exits the Winter Hexagon right next to Aldebaran, the orange eye of the Bull. Orion is of course to the left of Aldebaran in the APOD, while in Jimmy Westlake's image, Orion is below Aldebaran.

Oh, and while the yellow-white planet in Jimmy Westlake's image is Jupiter, the orange-colored planet (at far right) in the APOD is Mars.

Great APOD, and once again, thanks to Jimmy Westlake, too!

Ann