Space syllabus clarification (1 Viewer)

[Joshmosh2]

With the dotpoint "Discuss the issues associated with safe re-entry into the Earth's atmosphere and landing on the Earth's surface", would it specifically be referring to spacecrafts or space shuttles or maybe something else?

- making sure I get all the right technicalities for my phys assignment

 

[nerdasdasd]

With the dotpoint "Discuss the issues associated with safe re-entry into the Earth's atmosphere and landing on the Earth's surface", would it specifically be referring to spacecrafts or space shuttles or maybe something else?

- making sure I get all the right technicalities for my phys assignment

It's explained clearly in physics textbooks

Yes. It's referring to space crafts

 

[anomalousdecay]

http://www.boardofstudies.nsw.edu.au/syllabus_hsc/pdf_doc/physics_stg6_syl_03.pdf

Page 43

The next dot points after what you just said is:

"Identify that there is an optimum angle for safe re-entry for a manned spacecraft into the Earth's atmosphere and the consequences of failing to achieve this angle."

Pretty sure its just for a space craft/shuttle as they focus on it the next dot point. However it is a bit unclear.

Your teacher would have to be really unfair to consider anything else for the assignment. I mean its not like the BOSTES would ever ask "Discuss the re-entry and safe landing of a person parachuting from a low Earth orbit."

That is (a human or other type of body) the only thing other than a spacecraft of some sort which has entered the Earth from a low altitude, let alone a high one. Realy doubtful they would ask about a human or monkey parachuting in as no-one is even remotely taught about something like that and there is little evidence to it.

 

[astroman]

Discuss issues associated with safe re-entry into the Earth’s atmo- sphere and landing on the Earth’s surface (including “Identify that there is an op- timum angle for safe re-entry for a manned spacecraft into the Earth’s atmosphere and the consequences of failing to achieve this angle”)
Re-entry is a complex procedure due to the high velocities and temperatures encountered, as well as the fine balance of trajectory required to land safely. To land a space vehicle, the vehicle must firstly slow down, and secondly travel back down through the atmosphere. These are done simultaneously with atmospheric drag slowing the vehicle as it descends. The high velocity of the vehicle results in a great deal of friction, which heats the vehicle to up to 3000◦C depending on airflow. This necessitates highly temperature resistant shielding, usually ceramic or carbon based, that can withstand the temperatures and protect the rest of the vehicle as it descends. Modern designs also feature blunt noses and have the spacecraft descend belly-first, which ensures the majority of the vehicle is shielded. Without appropriate shielding, the vehicle will be unable to return, as recently seen in the 2004 Columbia space shuttle accident in which its heat shielding was compromised. Secondly, the angle of re-entry is critical. If the angle is too steep, the descent rate will be too fast, and the vehicle will encounter the higher density atmosphere closer to the Earth’s surface while it retains too much of its velocity. Higher density air provides more drag, which therefore decelerates the vehicle faster and leads to higher temperatures. This will result in at the very minimum excess g-forces for the crew, and at worst, the extra heating could destroy the entire vehicle. On the other hand, if the angle is too shallow, the spacecraft will retain too much of its velocity and exit the atmosphere by effectively skimming it, returning to space. The vehicle must have an angle between 5.2 and 7.2 degrees to make a safe re-entry. During re-entry, the high temperature of the spacecraft results in the air around it becoming ionised. This results in an ionisation blackout, with the ionised air blocking radio communication with the ground during re-entry. Although not a direct hazard, it can cause complications in the event of a safety issue arising during re-entry which could endanger the spacecraft. Finally, in order to land, the descent rate must be slowed dramatically. In the Apollo missions and with non-reusable space probes, parachutes are used to slow the descent to make a gentle landing. The space shuttle uses wings to generate lift, enabling it to glide to a gentle landing.
Remember- To re-enter, you need strong heat shielding and an approach with a specific angle of descent.

 

[dan964]

12. Safe Re-Entry
Discuss issues associated with safe re-entry into the Earth’s atmosphere

• Safe re-entry involves firstly the deceleration of the craft, by firing its retrorockets, which decreases the kinetic energy of the spacecraft, resulting in the craft moving to a lower altitude.
• Some of the factors that affect safe-entry include the orientation and shape of the craft, and the re-entry angle.

Air Resistance
• The friction between the spacecraft and the aircraft produces large amounts of heat, which need to be dissipated, to prevent the aircraft from burning up.
• Special materials are used to reduce the effects of this heat on the spacecraft and its occupants. Such materials have properties include poor thermal conductivity, thermally stable, high heat capacity and a good surface radiating ability. Materials suitable for this use include graphite, silicon dioxide and ceramics.
• The Apollo missions employ an ablative shield, which burns away taking the heat energy with it.
• The thickness of this shield had to be precisely calculated to ensure there was still some of it left when closer to the surface of the Earth.
• Modern spacecraft employ various technology including ceramic tiles and aluminium plates to reflect the heat, to minimise the effects of the friction-generated heat.
• The most vulnerable areas on the space shuttle are the nose-cone, the leading edge of the wings and to some extent the front underbelly of the shuttle. The surfaces of the vehicles in these areas are typically covered with strengthened graphite.
• Silica or ceramic tiles are used on the forward parts of the shuttle, and are painted black to increase its radiating ability. The doors are covered with a material called Nomex, and also with more tiles that are painted white to reflect heat.

G-Forces
• During re-entry, one of the issues associated is the g-forces experienced by the occupants of the spacecraft.
• If the descent is too rapid, then the occupants of the craft will be subject to too much g-forces, can result in loss of vision and eventually unconsciousness

Ionisation Blackout
• Another issue associated with safe re-entry is ionisation blackout, which is a period of time (about 12-15 minutes) that occurs when the aircraft loses communication contact with mission control after re-entering the atmosphere.
• The particles in the air surrounding the decelerating spacecraft is heated and ionised. This ionised gas is what is responsible for the communication blackout, as radio waves do not penetrate ionised gas.
• Although this is expected, if an emergency arises during this period, it presents a danger to the occupants of the spacecraft.

13. Re-entry Angle
Identify that there is an optimum angle for safe re-entry for a manned spacecraft into the Earth’s atmosphere and the consequences of failing to achieve this angle

• There is an ideal angle for re-entry. This is 6.2° ± 1°
• If the angle of re-entry is too shallow (such as 4°) the spacecraft skips off the atmosphere, meaning that the spacecraft may not have sufficient fuel for a successful second attempt.
• If the angle of re-entry is too steep (such as 8°) the spacecraft and its occupants being subject to high g-forces, and its speed would generate large amounts of friction, resulting in the spacecraft burning up in the atmosphere, due to the heat.

Note: This value was for the Apollo missions, it differs for different crafts depending on the shape of the craft and its re-entry speed.

 

[screwuhsc]

12. Safe Re-Entry
Discuss issues associated with safe re-entry into the Earth’s atmosphere

• Safe re-entry involves firstly the deceleration of the craft, by firing its retrorockets, which decreases the kinetic energy of the spacecraft, resulting in the craft moving to a lower altitude.
• Some of the factors that affect safe-entry include the orientation and shape of the craft, and the re-entry angle.

Air Resistance
• The friction between the spacecraft and the aircraft produces large amounts of heat, which need to be dissipated, to prevent the aircraft from burning up.
• Special materials are used to reduce the effects of this heat on the spacecraft and its occupants. Such materials have properties include poor thermal conductivity, thermally stable, high heat capacity and a good surface radiating ability. Materials suitable for this use include graphite, silicon dioxide and ceramics.
• The Apollo missions employ an ablative shield, which burns away taking the heat energy with it.
• The thickness of this shield had to be precisely calculated to ensure there was still some of it left when closer to the surface of the Earth.
• Modern spacecraft employ various technology including ceramic tiles and aluminium plates to reflect the heat, to minimise the effects of the friction-generated heat.
• The most vulnerable areas on the space shuttle are the nose-cone, the leading edge of the wings and to some extent the front underbelly of the shuttle. The surfaces of the vehicles in these areas are typically covered with strengthened graphite.
• Silica or ceramic tiles are used on the forward parts of the shuttle, and are painted black to increase its radiating ability. The doors are covered with a material called Nomex, and also with more tiles that are painted white to reflect heat.

G-Forces
• During re-entry, one of the issues associated is the g-forces experienced by the occupants of the spacecraft.
• If the descent is too rapid, then the occupants of the craft will be subject to too much g-forces, can result in loss of vision and eventually unconsciousness

Ionisation Blackout
• Another issue associated with safe re-entry is ionisation blackout, which is a period of time (about 12-15 minutes) that occurs when the aircraft loses communication contact with mission control after re-entering the atmosphere.
• The particles in the air surrounding the decelerating spacecraft is heated and ionised. This ionised gas is what is responsible for the communication blackout, as radio waves do not penetrate ionised gas.
• Although this is expected, if an emergency arises during this period, it presents a danger to the occupants of the spacecraft.

13. Re-entry Angle
Identify that there is an optimum angle for safe re-entry for a manned spacecraft into the Earth’s atmosphere and the consequences of failing to achieve this angle

• There is an ideal angle for re-entry. This is 6.2° ± 1°
• If the angle of re-entry is too shallow (such as 4°) the spacecraft skips off the atmosphere, meaning that the spacecraft may not have sufficient fuel for a successful second attempt.
• If the angle of re-entry is too steep (such as 8°) the spacecraft and its occupants being subject to high g-forces, and its speed would generate large amounts of friction, resulting in the spacecraft burning up in the atmosphere, due to the heat.

Note: This value was for the Apollo missions, it differs for different crafts depending on the shape of the craft and its re-entry speed.

i though the angle entry limit was from 5.7-7.2?

 

[iStudent]

i though the angle entry limit was from 5.7-7.2?

Same thing as 6.2+-1

 

[tyrone97]

I know this thread is 1 month old, but for the sake of anyone reading this later on down the road the allowable angle of re-entry varies depending on the design of the space shuttle and how its going to enter (eg. ballistic re-entry with no retrofired thurst engines, or space shuttle that does use retrofire). - Source: In2Physics