Orion shielding from radiation.

[Gazpar]

What does this means? Didnt NASA solve the radiation problem already in 1969?
Or is more problem for electronics than human safety? I though they had the data about radiation levels of the belts.

[grmcdorman]

As I understand it, it's a duration question: Orion is intended for longer-duration missions. The Apollo capsule was exclusively intended for a short-duration journey to the Moon and back, and nothing else. It also may not have had much margin in the event of a major solar flare (as higher risk levels were acceptable not only in the Apollo program, but in society as a whole at the time).

[Gazpar]

As I understand it, it's a duration question: Orion is intended for longer-duration missions. The Apollo capsule was exclusively intended for a short-duration journey to the Moon and back, and nothing else. It also may not have had much margin in the event of a major solar flare (as higher risk levels were acceptable not only in the Apollo program, but in society as a whole at the time).

What about the electronics part of the apollo spacecraft of that time? Maybe that part was not too susceptible as Orion cutting edge computers onboard.
I heard also that Orion will pass through the thickest parts of the belt(deep space travel) as opposed to apollo, which went through the thin parts of it.

[grmcdorman]

Both duration and sophistication. The electronics from the Apollo era was much less susceptible, as you imaging (look up "rope core" some time); however, mission duration (and solar flares) are again a factor.

I suspect the Orion electronics, by the way, will not be cutting edge. Spacecraft electronics needs to be robust, not cutting edge.

I understand from other posts here (and from the Planetary Society's recent LightSail test) that modern satellite electronics is expected to have failures. The hardware must be designed to be fault-tolerant, i.e. recover from faults and continue to operate.

I don't know about the transfer orbits, though; perhaps someone else can answer that.

[Bob B.]

It is my understanding that Orion's trajectory took it through regions of the Van Allen Belts that were far more intense than the regions through which Apollo flew.  I don't know Orion's trajectory exactly, but I do know that the Apollo trajectories reduced the radiation exposure by about 95% versus flying right through the heart of the radiation belts.  Furthermore, Orion was in orbit and moving more slowly than Apollo, thus it spent more time in the higher intensity lower regions of the belts.  Apollo was on a high speed outward trajectory that carried it through the worst part of the belts very quickly.  Orion's computer is also more sensitive to radiation than Apollo's.

[smartcooky]

The Apollo Guidance Computer used RTL (resistor-transistor logic) integrated circuits. These were not susceptible to static, cosmic rays or EM radiation to the same degree that the later CMOS chips were.

[Gazpar]

The Apollo Guidance Computer used RTL (resistor-transistor logic) integrated circuits. These were not susceptible to static, cosmic rays or EM radiation to the same degree that the later CMOS chips were.

Yeah, that would make sense but is there any reason why RTL are not susceptible to static, cosmic rays or EM radiation than CMOS chips?

[Allan F]

The actual part of the component which makes the connection is much larger, and the erosion from radiation will have to destroy much more material, before the component is inoperative.


Like killing a bridge with rifle fire versus killing a power line.

[gwiz]

I understand from other posts here (and from the Planetary Society's recent LightSail test) that modern satellite electronics is expected to have failures. The hardware must be designed to be fault-tolerant, i.e. recover from faults and continue to operate.

The LightSail mission was saved by this.  Its computer shut down because of an overlooked problem with the software, but a few days later it got a radiation hit that caused a re-boot.

[ka9q]

The Orion flight was an engineering test. No crew was on board, so they could afford to take larger risks to stress the systems than would be encountered in a normal mission. One of those greater risks was the radiation environment, which was considerably more intense than Apollo saw on a trip to the moon.

And yes, the Apollo hardware was inherently more radiation-resistant than modern electronics. Much of the logic was done purely in hardware with diodes, discrete transistors, mechanical switches and relays. The SSI (Small Scale Integration) RTL (Resistor-Transistor Logic) integrated circuits in the guidance computer had very large transistors, which means radiation has to deposit considerably more energy to cause a temporary upset or destroy the device.

[Jason Thompson]

Didnt NASA solve the radiation problem already in 1969?

Yes, for a short mission of two weeks' duration.

I though they had the data about radiation levels of the belts.

Would you want to rely on shipping forcasts from fifty years ago when you embark on a trip across the sea?

A few bullet points to consider:

1: All data are valuable, and the more up-to-date the better.

2: Modern electronics respond differently to radiation than the hardware used in Apollo does.

3: Radiation damage is cumulative.

4: The probability of encountering a major solar event increases with duration of the mission.

5: Orion is planning missions of much longer duration than Apollo.

All of which boils down to the simple fact that the data collected about the radiation problem, and the solutions devised, for the Apollo programme are inadequate for the very different planned Orion missions.

[Echnaton]

Part of the concept of Orion is to make it reusable.  That is a significant difference between the mostly one time use design of the Apollo missions.  Although IIRC there was some reuse of Apollo equipment.  Designing in longevity of human rated equipment from the start means more a more robust design than was necessary 40 years ago and more testing.  What better way to do the testing than to put it through a harsh environment.   Orion is really a quite different system from either the Apollo CSM or the Shuttle, with different mission goals and requirements.  Besides, nothing is ever permanently solved. 

[JayUtah]

Many of Apollo's critical control systems (e.g., Earth Landing System) were relay logic.  This is due in part to its being impervious to radiation and a host of other hostile influences, but also in part to the long experience in designing such systems.  Solid-state logic was still in relative infancy and not fully trusted.  Relay logic at that point had a 60-year design pedigree and had all the bugs (literal, in fact) worked out.

The Apollo shielding factor was almost entirely accidental.  Which is to say, no part of the Apollo spacecraft was designated as radiation shielding.  All the shielding effects came from things that were already there for other reasons.  They added up to a robust 7 g cm^-2, which turns out to be sufficient for an Apollo-type mission barring catastrophic solar activity.  Orion is intended for more extensive missions.

[Gazpar]

Could it be that orion passed through the more dense parts of the belts, opposed to apollo? Im trying to find a source for this

[Bob B.]

Van Allen belt radiation consists of high-energy electrons and protons in the inner belt, and high-energy electrons in the outer belt.

The most energetic electrons encountered along the trajectories flown by Apollo have an energy of about 7 MeV.  The 7 g/cm shielding provided by the CM hull is about twice that needed to completely stop a 7 MeV electron.  Electrons, therefore, were of no concern to Apollo as they were virtually all blocked by the hull. 

At a given energy, protons are less penetrating than electrons.  Therefore, virtually all protons on the low end of the energy spectrum were easily blocking by the spacecraft shielding.  The only real concern from a radiation standpoint were the most highly energetic protons, which can exceed 100 MeV.  These protons could penetrate Apollo's shielding and potentially cause damage.  Fortunately, high-energy particles are far fewer in number than low-energy particles (by many orders of magnitude).  Apollo also used a highspeed injection that allowed it to pass by the inner radiation belt in just a manner of minutes.  Also note that the inner radiation belt is a torus (doughnut shaped) that is most intense near the center and weaker near the edges.  Apollo flew inclined trajectories that bypassed the intense middle regions and grazed along the weak edges.  All of this adds up to a radiation condition that was not of significant concern.  Apollo passed through the region quickly and through the weak outer edges where there just weren't enough high-energy protons to cause damage.

The Orion test flight is an entirely different animal.  After performing one low orbit of Earth, Orion fired its engine to alter its trajectory.  The apogee was raised to 5790 km and the perigee was lowered to -29.8 km (below the surface of Earth).  This orbit allowed Orion to pass through the inner Van Allen belt to test the spacecraft's radiation resistance, and then to make a high-speed reentry to test the spacecraft's thermal protection.

The inner Van Allen belt's altitude above Earth's surface ranges from about 1000 km to 6000 km.  Therefore, the entire part of Orion's orbit above 1000 km was within the radiation belt.  From Orion's orbital parameters, I calculate that it spent 118 minutes in this region of space.  For comparison, Apollo passed through the same range of altitudes in just 17 minutes, once on the way to the Moon and once on the way back, for a total of 34 minutes.  The duration of Orion's passage through the inner radiation belt was about 3.5 times longer than Apollo's.

It must also be noted that Orion's inclination was 28.8 degrees, which is lower than the inclinations used by Apollo.  Orion was therefore closer to the more intense middle region of the radiation belt.  More importantly, the portion of Orion's orbit above 1000 km spanned an arc of 229 degrees.  This means that Orion had to pass through at least one of its nodes while within the radiation belt.  The significance of this is that at some point during its passage through the radiation belt, Orion had to cross the latitudes at which the radiation belt is its most intense.

I don't have all the specific data needed to make a detailed quantitative analysis of Orion versus Apollo.  However, based on the orbital data that I do have and my past experience studying the radiation belts, I think it is safe to say that Orion's radiation exposure was dozens of times greater than what Apollo was exposed to.