Comments by "H. de Jong" (@h.dejong2531) on "Things We’ve Never Seen: The James Webb Space Telescope Explores the Cosmos" video.

  1. CGI is the best way to explain how the telescope deployments work.
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  2. Hubble was launched in 1990, SOFIA in 2007. If that's the quality of the information you're getting, you need a new source of information.
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  3. No. Anything we can build today is far too small to have a measurable effect on the magnetic fields of the Sun or Earth.
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  4. it is refuelable. The only thing we don't have yet is a spacecraft that can approach JWST without damaging the sunshield.
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  5. We 'can't' in the sense that we don't have hardware sitting on the launch pad ready to fly a manned mission to the moon. The rocket and spacecraft we need for that are in development at the moment.
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  6. it's an area where the gravitational fields of Earth and the Sun are in equilibrium. You can draw orbits around L2 where the forces balance out. JWST will also use its thrusters regularly to stay in orbit.
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  7. Almost right: JWST will be in a large orbit around L2.
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  8. Check out the next telescope proposal: LUVOIR.
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  9. You mean, collect particles from the solar wind and store those for use as propellant? The solar wind doesn't provide enough matter to do that.
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  10. There's a radio transmitter on JWST, with a dish antenna pointed at Earth. Twice a day, NASA's Deep Space Network is used do download information from JWST and upload new commands. These downloads take up to 4 hours. The DSN has large dish antennas (34 m and 70 m diameter) in 3 stations: Goldstone, USA, Madrid and Canberra. These antennas are equipped with receivers that are cooled to around 4 K, to reduce their noise to the absolute minimum. JWST transmits in the Ka-band (around 26 GHz), at 3.5 Mbyte/s. We don't need repeaters with an antenna this large.
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  11. Earth weighs 10e24 kg. JWST weighs 10e3 kg. The amount of material removed is negligible.
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  12.  @user-Rockstar1  We have placed over 12000 satellites in orbit over a period of 60 years. Rockets don't go straight up because they have to orbit Earth, i.e. fly parallel to Earth's surface. Most of a rocket's job is to build speed (8 km/s) not altitude (200 km is enough in many cases).  Airplanes fly above the location the Bible gives for the firmament. Those are thousands of flights a day for a century, There is no evidence in favor of a firmament. Light from space reaches us unimpeded. We can send radio waves through it, we can send objects through it, etc.
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  13. no. The sunshield also covers the Earth and Moon (2 big sources of heat that have to be avoided).
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  14. They use reaction wheels for pointing, and magnetic torque bars to desaturate the reaction wheels.
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  15. The world is not flat. The curvature of the Earth is 8 cm per km (about 4" per mile), which is too small to see when you stand at ground level. You can easily measure this using only basic tools, if you live in an area of level ground. Hills have much larger curvatures than 8 cm/km so in hilly areas measuring Earth's curvature is more difficult. You can see the curvature of the Earth with the naked eye from an altitude of about 15 km. If you take a photo at ground level, in an area where you can see the horizon, and you measure the photo, the curvature shows up as well.
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  16. Biologists have studied that question. It's much harder for silicon to form complex molecules. Among all of the millions of species on Earth, 0 are silicon-based. So we have pretty good indicators that carbon-based life is more common than silicon-based life.
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  17. A successor to Hubble is being planned, but that will be a separate mission (LUVOIR).
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  18. No planet that close is going to be invisible. We can see Venus with the naked eye, we could see a planet in a similar orbit out of the ecliptic plane just as well.
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  19. A solid enclosure would have made the telescope too large to fit on the Ariane 5. You're overestimating the amount of space dust JWST will encounter.
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  20. that depends on the target: an image of Jupiter can be done in a few seconds, an image like Hubble's Deep Field will take days.
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  21. NASA publishes the raw data for all of their science missions.
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  22. JWST is a joint NASA-ESA-CSA project. The launch was part of ESA's contribution to the cost.
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  23. Yes, it has a refueling port. What we don't have yet is a spacecraft that can safely approach JWST without damaging the sunshield.
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  24. the 'space is very empty' comment was about dust, meteors etc. The average density of space in our solar system is 1 atom per cm3. You're right, there are lots of stars, but they're very far apart.
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  25. JWST's cameras would be damaged by the heat if they were aimed at Earth. Luckily, we don't need JWST for this. There's loads of satellites closer to Earth that provide images of Earth every day. JWST will probably be used in the search for planet X (which is far away in the outer solar system, if it exists). We're certain Nibiru does not exist - we regularly look at the area where the legend says it is, and there's nothing there.
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  26.  @mikecolquhoun1674  It has solar panels to power the electrical systems on board. These systems require up to 2 kW of power. If you want to use fossil fuels to produce 2 kW for 10 years, that's 175 MWh, at 200 g/kWh is 35 tons of fuel, and you need oxygen as well. The solar panel weighs closer to 35 kg. With 35 tons of fuel we wouldn't have been able to launch JWST - there's no rocket today that can lift a payload that heavy.
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  27. Yes, you can. Gravity acts on gases, just like it acts on liquids and solids.
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  28. An exoplanet will be a single pixel - so all the light coming from that planet will be mixed up. I don't think we can extract an aurora from that.
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  29. And yet billions of vaccination later, we're all still alive.
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  30. JWST can be refueled, we just haven't built a spacecraft that can do this safely yet.
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  31.  @dougwedel9484  there's a couple of reasons it'll take 6 months. 1. cooling down the telescope takes a long time. They have to do this slowly, to make sure any gases escaping from the telescope don't condense on the mirrors or the imaging sensors. For the next month, heaters will keep these elements warm. 2. the mirror positions have to be finetuned: they must match within a few nanometers. AFAIK, JWST will be inserted into orbit by the end of January.
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  32. at 100 jupiter masses, you're already in 'small star' territory, instead of 'large planet'.
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  33. JWST can be refueled. The hard part is to design a spacecraft that can approach JWST without damaging its sunshield. This is a lot easier with a lightweight spacecraft than with a massive Starship.
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  34. We're looking at the closest planets for signs of life, so up to 1000 lightyears.
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  35. it's kapton with a metallic layer. Spacecraft are wrapped in this because it's an excellent insulator, protecting the spacecraft from the huge temperature variations in space (+100 ºC in direct sunlight, -200ºC in the shadow).
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  36. They're going at a slow speed because JWST has no thrusters on the side facing away from the Sun. So they can't slow down when they get to the target orbit. The speed slowly drops off as it gets farther away from Earth (due to Earth's gravity), they've calculated the speed to reach 0 at exactly the right time.
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  37.  @goobytron2888  I've done a lot of reading about JWST over the years. You're right, when JWST was released from the second stage it was moving at 22000 mph, above escape velocity. But escape velocity doesn't mean Earth's gravity is no longer a factor. Compare it to throwing a ball straight up: its velocity decreases during the climb, until it reaches 0. In physics term, kinetic energy (speed) is converted to potential energy (altitude). JWST is doing this too: converting that 22000 mph into the potential energy of an orbit at 1.5 million km altitude.
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  38. no. Images will be analyzed on the ground, not onboard.
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  39. JWST is designed to be refueled. JWST uses reaction wheels to point the telescope, occasionally these have to be 'reset' and that requires fuel. It also needs fuel to correct its orbit about once a month. Without fuel the spacecraft will start drifting away from the L2 point. The end of the mission will be when the antenna can no longer be pointed at Earth. The telescope uses liquid helium for cooling, with a cooling system to keep this helium cold. This shouldn't run out any time soon.
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  40. Draw a line from the Sun to Eath. Then continue this line on Earth's night side, for 1.5 million km. That's where the L2 point is. The sun won't be between JWST and Earth.
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  41. 10 days after launch, the cold side is already at -233 ºC. I don't think it'll take 6 months to cool down to final temperature: in about 2 weeks the calibration process starts. That will take a few months.
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  42. That's Murphy's law, not Moore. They spent years testing every aspect of the telescope.
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  43. JWST IS using solar energy.
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  44. Genesis 1:20: 'and fowl that may fly above the earth in the open  of heaven.' If birds can fly IN the firmament, that makes it unlikely a solid structure is meant. Genesis describes the world in terms the people of that time could understand.
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  45. We can measure the speed of stars and galaxies; they're all moving away from us, so the universe is expanding.
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  46. Space is expanding, but objects in space can also move. Andromeda is moving toward us faster than the space between us and Andromeda is expanding.
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  47. It takes more than one 1.5 hour webcast to explain everything about JWST. The information you want can be found elsewhere.
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  48. Ion engines are really good when you need lots of speed on a small amount of fuel, but the engines themselves are heavy. So for small corrections like JWST needs, ion engines are usually not lighter than hydrazine engines.
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  49. There's thousands of images that show this, going back to the 1960s. A selection: @
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  50. The telescope is designed to be refueled. Making the instruments serviceable would have added too much weight and we wouldn't have been able to launch it.
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  51. Good question. The fingerprints are still there and recognizable: for each element or molecule, you get a bunch of spectral lines and the distances between them match what we measure in a lab: It's just that the entire group of lines is shifted towards the IR. That's actually how we measure redshift: we take a spectrum, and try to match it to known elements. Then we measure where the lines occur, calculate the difference with our lab fingerprint and we know how much it has been shifted.
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  52. just gravity. It's in an unstable orbit and needs regular corrections to stay in that orbit.
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  53. Layer one reflects most of the incoming heat, but transfers some of it and reradiates on the other side. Layer 2 reflects most of this, but transfers some of it and reradiates on the other side, etc. 4 layers is enough to get the insulation they need, a fifth layer was added for redundancy.
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  54. JWST is at the L2 point. It will never be between us and the Sun. To block the Sun, you need an object 3400 km wide, like the Moon.
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  55. The chance of that is very low: space is empty. The telescope can't protect itself: it has no way to detect asteroids. We have asteroid monitoring systems on Earth, and if a big asteroid were to come near the telescope, we could command evasive maneuvers from Earth.
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  56. For radiation, there are 2 important variables: 1. the radiation intensity 2. the amount of time you are exposed to this intensity. You can multiply these two and get the total radiation dose. Humans die if they receive a dose of about 300 Rad. In 1958, James van Allen and his team discovered the belts that were later named after him. He also measured the radiation intensity. This is what he found: in the part of the belt where the intensity is highest, it is high enough that if you stay for about a week, you receive a lethal dose. So for the Apollo missions, the trajectory was designed to minimize the amount of time spent there. When the Apollo astronauts flew through the van Allen belts (which took about an hour), they received a dose of radiation of about 2 Rad, or ~1% of a lethal dose.
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  57. it's currently very expensive to land large amounts of material on the moon.
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  58. You see Venus at dawn or dusk, i.e. close to the Sun, right where the heliocentric model predicts it will be. There's loads of photos that show Hubble in space.
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  59. Space is really empty. So we can move fragile structures in space without damaging them.
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  60. can't do that, that would expose the instruments to the Sun and overheat them. NASA occasionally does a life feed showing Earth from the ISS. Worth watching.
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  61. ​ @marcusaquarius1585  The astronauts adjusted the exposure time to get their main subject (Moon surface, astronaut activities) well-lit, which means the stars don't show up. You can try this for yourself if you have a camera with manual settings: take a photo during the day, with exposure time and diaphragm set appropriately. Use the same settings to take a photo of the night sky. No stars will show up, because the exposure is far too short. There are photos of Earth taken from the Moon surface, but most of the Apollo photos (and video) that show Earth were taken from lunar orbit.
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  62. CGI is useful to explain how the telescope works.
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  63. not quite. Previous IR telescopes used a large tank of liquid helium that slowly evaporated. This evaporation (which had to be vented) kept the remaining helium at 4 K, but it meant the mission ended when the helium ran out. Hubble doesn't use cooling. JWST has an active cooling system: a device that removes heat from the liquid helium, so the helium doesn't evaporate. The device that has to be cooled is the image sensor (CCD).
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  64. Data is usually published after a few months (to give the mission team a first chance to look at the data).
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  65. 'no air in space' is generally correct, however the atmosphere doesn't end abruptly. At 100 km altitude, air pressure is about 10e-15 bar, and it keeps dropping off as you get higher. You have to be above 1000 km before there's no noticeable drag. The ISS (to 400 km) loses several km of altitude per month due to drag, so every few months it has to be boosted to a higher orbit.
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  66. Yes, the simulation is correct. JWST will be in full sunlight, so it can use solar power.
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  67. don't be ridiculous. A sun simulator that can 'cover up' a lunar eclipse has to produce as much light as the sun itself, over an area 3400 km across. That takes 10e21 W, or a billion times more power than the entire Earth uses. Eclipses also are not occurring more, they continue to have the same frequency as they've had for thousands of years.
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  68. electrical power is from solar panels. The telescope also needs occasional course corrections using rocket thrusters. The thruster fuel is the limiting factor for the mission, but the spacecraft is designed to be refueled.
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