Discussion in a previous post centered on getting to space and into an orbit near Earth. This post is about how spacecraft return from orbit. Some returns are under control and some are not.
Launch to orbit requires giving a spacecraft a large amount of kinetic energy of motion (KE) and a large amount of gravitational energy (PE) due to its altitude. The large amount of work done to gain those energies comes from the potential energy released by an engine(s) as fuel burns. Once in orbit with engine(s) off, the total of those two energies (KE+PE) stays constant except for the small decrease due to the small atmospheric drag at high altitudes. If the orbit is a circle the two energy quantities are unchanging.
If the orbit is an eccentric ellipse, the quantities do change but not their total. The next graphic shows an eccentric orbit of an Earth satellite. When it passes closest to Earth (perigee), the KE is at its maximum value and the PE is at its minimum. Font size was changed to illustrate their inequality. When at its farthest point in orbit (apogee), it is going slowest with minimum KE and is at its highest altitude with maximum PE.
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Take a time-out from the news of the day or your busy routine. Tour some of the interesting features of our Moon as presented by the NASA Goddard Space Flight Center/David Ladd. Best viewed in HD by using the gear button at the bottom right of the video window.
The concepts are simple to place a satellite or a manned space capsule into orbit near the Earth. But, they are very difficult to achieve.
- Engines must exert a lot more upward force than the downward force of the weight of the fueled rocket.
- After lift-off, gradually point the rocket more horizontally as it moves faster.
- Jettison the empty 1st stage. The 2nd stage engine(s) continues to speed up the payload horizontally.
- Shut down the engine(s) to allow the payload to coast in circular orbit when at altitude of about 120 miles (~200 km) and speed of about 17,500 mph (~ 28,200 kph).
The orbit drawn here to scale in yellow allows the spacecraft to coast for some time above most of the atmosphere. But it will not coast forever. The thin atmosphere will gradually bring it down.
Earth image from NASA
The U.S. started launching rockets from Cape Canaveral Florida in 1950. The European Space Agency launches from Guiana Space Centre northwest of Kourou in French Guiana. France established that space port in 1964. Each site has open water to the east avoiding the danger to populated areas. Each site uses the speed boost from the eastward rotation of the Earth to assist launch speeds. Guiana is near the equator and moves east about 1000 mph. Cape Canaveral moves east over 900 mph. With the better technologies today, rockets can be launched to orbit from about anywhere and in non-east directions such as for polar orbits.
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The sun’s output in the visible spectrum peaks around yellow. Our eyes are most sensitive to that part of the visible spectrum. The sun also radiates in a broad range of other wavelengths invisible to our eyes. Each comes from dynamics taking place on the surface and in the atmosphere of the sun.
I’ve written about NASA’s Solar Dynamics Observatory (SDO) earlier in a previous post. SDO observes and images the sun several times a minute at ten different wavelengths to give a more complete picture of the activity at and near the surface. A description of those wavelengths is available here. I used the images from the SDO site to render this image of the sun at those ten wavelengths. The yellow center represents the sun’s surface. Each ring of color is at a higher altitude and temperature in the atmosphere of the sun.
Original images used from: NASA/GSFC/Solar Dynamics Observatory
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The JUNO spacecraft continues its mission of very close flybys of the cloud tops of Jupiter. The most recent pass was on 19 May 2017. Images downloaded from the JunoCam instrument were made available to the public. I downloaded two sets in red, green, and blue filtered grayscale. Each set was combined into color versions using Photoshop and techniques described in a previous post. The colors are my interpretation and not necessarily real.
The Juno spacecraft successfully made a third close flyby of Jupiter on 11 Dec 2016. It was initially captured in orbit on 4 July 2016 as I noted in this blog post. The next close pass will be in early February. This brief animation illustrates a close flyby as Juno skims barely above the cloud tops of Jupiter.
On board Juno is a video camera called JunoCam. During the passes, JunoCam captures images which are sent to Earth. They are available to the public for download and processing. NASA hopes the public will use the images in creative projects. The creations can then be uploaded back to the JunoCam site for others to view.
I downloaded three images in Red, Green, and Blue of the south polar region of Jupiter. The video above shows Juno approaching over the north pole, passing very close to the equator, then receding below the south pole with each orbit. My three images were taken when Juno was directly below Jupiter’s south pole.
Using Photoshop, I opened the three RGB files, adjusted them for intensity, them combined them into this color composite. The program allowed me to adjust the saturation of many different colors across the face of the planet for enhancement. I uploaded it back to JunoCam. The colors are not realistic. But they do show the differences and circulations more readily. That was fun.
On 27 August 2016, Jupiter was involved in two interesting events. At around 7:44 am CDT the Juno spacecraft made a very close and fast flyby of the planet going 130,000 mph. It came within 2600 miles of the cloud tops, the closest to the clouds for the entire mission of 35 more orbits. NASA reported the entire suite of scientific instruments was turned on and functioned well. Data will be returned over the next days and weeks.
The image at left is a view of the north pole of Jupiter just prior to the flyby. The polar orbit is a first for Jupiter exploration.
According to Scott Bolton, principal investigator, “We are getting some intriguing early data returns as we speak. It will take days for all the science data collected during the flyby to be downlinked and even more to begin to comprehend what Juno and Jupiter are trying to tell us. We are in an orbit nobody has ever been in before, and these images give us a whole new perspective on this gas-giant world.”
High resolution images will be released in the next two weeks.
More information and details about the Juno mission are available at this previous post.
At sunset also on the 27th, Jupiter and Venus aligned about 1/2˚ apart low in the western sky. That is the width of a full-moon. The dense cloud cover earlier in the day gave way to some partially clear sky for the evening show. The air was laden with much moisture and cloud remnants. The planets were visible. But, hazy conditions made their images not sharp and clear. I couldn’t wait for darkness because the clouds were approaching. Below is a wide view and a fully zoomed view. Venus is the upper and brightest of the two.
Jupiter aligned with Venus but was much more distant, small and dim.