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67 votes
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Are there any space probes or landers which regained communication after being lost?

Well, it is very common indeed to regain communications with a space probe after losing contact. In fact, communications are generally not continuous for the entirety of any mission. These are ...
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64 votes

Why it's news that SOFIA found water when it's already been found?

This discovery is news because the water found is in a sunlit area, the Clavius Crater. Previous water discoveries were all in 'cold traps', which are areas where sunlight cannot reach, so water ...
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55 votes
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Has any space agency saved Earth from a major calamity any time?

More fundamental, and a question if it counts as a 'space agency' act being NOAA led but weather satellites not only reduced the fatalities associated with weather data collection but increased the ...
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50 votes
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What kind of orbit makes this wave shaped ground track?

An elliptical one. The Wikipedia page you link gives a signfiicantly different apogee and perigee and a period of 20.8 hours. So, on average, it moves West to East a bit faster than the Earth does, ...
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45 votes

Has any space agency saved Earth from a major calamity any time?

Ozone depletion was hypothesized and first measured without the means of satellites according to the wikipedia article. However, satellite data was apparently very helpful in showing the scope/size ...
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39 votes

Has any space agency saved Earth from a major calamity any time?

Has any space agency saved Earth from a major calamity at anytime? There are historians who believe that the US–Soviet and US–Russian collaboration, for example in the Apollo–Soyuz Test Project, the ...
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34 votes
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Why does the Indian PSLV rocket have tiny boosters?

Why would these be used instead of just using a larger first stage? Strapping on differently-sized boosters allows variance in payload mass without redesign of the first stage. The PSLV has flown with ...
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31 votes
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Why do some rockets not ignite all their engines during liftoff? (GSLV MK3 LV)

Besides limiting aerodynamic stress and drag losses as you and Antzi mention, using the core engine only at high altitude means the engine can be optimized for low-pressure use by putting a larger ...
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27 votes
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Why is China still not invited to the ISS? (Or, why do certain countries not get invited/rejected to work on the ISS?)

China has nothing to prove in this case, as it asked to be part of the International Space Station. This request was shut down by the US Government, which now prevents NASA from working with any ...
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27 votes
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Why it's news that SOFIA found water when it's already been found?

It is news because the 6.1 $\mu$m wavelength measured is unique to $\rm{H_2O}$. All prior evidence included $\rm{OH}$ groups as well, thus did not show clear proof of presence of "$\rm{H_2O}$&...
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21 votes

Cheap cost of Mangalyaan

Comparing Mangalyaan (MOM) to Maven there's a significant difference in mission, scientific capabilities and operational lifetime. Maven's primary purpose is to study the martian atmosphere, whereas ...
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20 votes

Are there any space probes or landers which regained communication after being lost?

Are there any space probes\landers which regain communication after being lost? IMAGE Contact was lost with IMAGE on December 18, 2005, 07:39 UTC and it was ...
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18 votes

Why do some rockets not ignite all their engines during liftoff? (GSLV MK3 LV)

Your assumption that we need max thrust at takeoff is partially wrong. Although right at takeoff you do want max thrust, it might be counterproductive short after: Your rocket and payload are Max G ...
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17 votes
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Cheap cost of Mangalyaan

As per "From lighter rocket to slingshot, Isro innovates its way to Mars" from Hindustan Times: The main reasons for the low cost are: Low labour cost. In India scientists are working with very low ...
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  • 486
17 votes

Has any space agency saved Earth from a major calamity any time?

As yet, no space agency has blasted anything that may have posed a hazard to Earth. One of the issues with blasting such hazards is the numerous fragments of the blasted object may pose a greater risk ...
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16 votes
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Why would thermal imaging be used to locate the Chandrayaan-2 lander?

It was not a thermal image at all. It is an optical image that has been captured by Orbiter of the lander spot and not thermal image as reported by others media houses. OHRC is same like our ...
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16 votes

Has any space agency saved Earth from a major calamity any time?

Like diverting meteor path away from Earth or blasting giant asteroid which was expected to impact Earth etc. Not yet. However, later this year (between 26 September 2022 and 2 October 2022), NASA's ...
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13 votes
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Why does PSLV use four stages to get to LEO, and why do they alternate solid, liquid, solid, liquid?

PSLV is a bit of a weird duck because it's a transitional step from small solid-rocket designs to larger ones that rely more heavily on liquid rocket engines with higher specific impulse. It doesn't ...
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13 votes
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What are the advantages of air lit solid boosters in PSLV XL?

This probably has to do with optimizing the launch efficiency of the rocket. More specifically, a rocket has two goals: Get out of the atmosphere Reach orbital velocity The second step can't really ...
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12 votes

Why is China still not invited to the ISS? (Or, why do certain countries not get invited/rejected to work on the ISS?)

This is will be a very humble answer and an overview of events that caused the complication. It has been more of a political issue rather than technical issue. U.S. congress always have wanted to ...
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  • 561
12 votes
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Is there any way to determine the fate of Chandrayaan-2?

I think a somewhat reasonable first-order analysis would look at the fates of similar hard impact failures on the moon and in deep space. The most immediately relevant is the failure of Israel's ...
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10 votes
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GSLV MK2 vs Falcon 9 - Reasons for Huge performance difference

The biggest factor is probably the "inside-out" staging design, where the solid core burns out but is not jettisoned, while the liquid boosters continue to run. Spaceflight101 gives the empty mass of ...
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10 votes
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Might ISRO's 2018-004 launch be at least a technical violation of the Outer Space Treaty by India?

Sorry for being a few weeks late to this, but hopefully I can shed some light on how to think about it. The ISRO launch of these satellites is legally problematic in several ways. First, and as ...
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10 votes
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What are the falling parts in this ISRO rocket launch?

According to this article, those are insulation panels, and they're simply lightweight enough to not damage the rocket at the relatively low speeds it's moving in the initial seconds of flight. The ...
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10 votes

Why is the Duration of Time spent in the Dayside greater than that of the Night side of the Moon for Chandrayaan-2 Orbiter?

The degree of orbital shadowing experienced by an orbiting object with small orbital altitude is determined by its beta angle (normally used in reference to LEO objects but the concept applies to ...
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9 votes
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What have been India's Mars mission's benefits to science?

Other than taking images of Mars' moon Deimos far side (something not done in decades) not much has been attributed to MOM yet. The key here is to remember that the the orbiter likely won't discover ...
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9 votes
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How was it difficult for the PSLV to launch a record of 104 satellites?

The key phrase is "satellites separated from the final stage safely without colliding into each other" Let's break that into two pieces: Satellites Separated From Each other- In order to do this, it ...
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9 votes

Might ISRO's 2018-004 launch be at least a technical violation of the Outer Space Treaty by India?

The satellites were launched on a vehicle operated by the indian government, with (at least implicit) permission of India. This is clearly not a violation of the Outer Space Treaty, it only means ...
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9 votes

Why does the Indian PSLV rocket have tiny boosters?

The answer already posted is excellent. All I want to add is a follow-up question you might want to ask, and my answer to it. Q: OK, so those in particular aren't boosters. But would it ever make ...
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8 votes
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What does CLG INIT mean?

"CLG INIT" stands for "closed loop guidance initiation", and means that the launcher is switching into a mode where it actively steers based on its current trajectory rather than a fixed, ...
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