Space Academy for Educators

Ablative Shielding

Space Academy for Educators

2 hours

Overview:

Trainees will learn about how heat transfers and how heat tiles and ablative systems protect space craft. In the activity, trainees will attempt to create an ablative heat shield to protect and egg utilizing information learned in the power point.

Objective:

Describe how heat tiles protect the orbiter.

Define ablation, convection, conduction and radiation.

Create a thermal protection system that uses these concepts to protect and egg.

Collect data to analyze and share results.

Educational Standards:

Next Generation Science Standards: 3-5 Engineering Design: ETS1-1, ETS1-2, & ETS1-3; MS Engineering Design: ETS1-1, ETS1-2, ETS1-3, ETS1-4, Energy: PS3-4.

Common Core State Standards: Key Ideas & Details: ELA-Literacy.RST.6-8.3; Presentation of Knowledge and Idea: ELA-Literacy.SL.3.4, ELA-Literacy.SL.4.4, ELA-Literacy.SL.5.4, ELA-Literacy.SL.6.4, ELA-Literacy.SL.7.4, & ELA-Literacy.SL.8.4.

Materials:

For the briefing:

·  Projector

·  PowerPoint

For shield testing:

·  Pre-fabricated test stand

·  Propane tanks (2)

·  Propane igniter

·  Eggs (1 per sub-team)

·  Flame resistant mat (Optional)

·  Safety cones

·  Safety glasses

·  Safety gloves

·  Fire extinguisher

·  Infrared Thermometer

Shield construction materials:

·  Data / scoring sheets

·  Cotton balls

·  Large steel (3” x 3”)

·  Uncooked lasagna noodles

·  Spackle

·  Cork (3” x 3”)

·  Sponges

·  Steel wool (No soap added)

·  Acrylic yarn (1’ sections)

·  Aluminum foil (4” x 4”)

·  Aluminum mesh (3” x 3”)

·  Copper mesh (3” x 3”)

·  Cotton yarn (1’ sections)

·  Felt (3” x 3”)

·  Paper (4” x 4”)

Activity:

·  Early Preparation (? min)

Pre-Activity Prep – done before the day of the activity. Time can vary on skill / tools. Purchase and cut down supplies as needed. This is also the time to prepare the test stand if needed – directions are in a PowerPoint titled “How to build the test stand with photos” in the same GoogleDocs folder.

·  Introduction (30 min)

Discuss thermal protection systems.

The trainees may already know that the shuttle and other spacecraft travel at 17,500 mph (or 28,000 kmph). When the spacecraft reenters, it uses the air to help it slow down. This heats the air immediately around the orbiter to temperatures of in excess of 3,000ºF (1,649ºC), hot enough to melt steel.

On the orbiter thermal protection is provided by tiles – about 24,000- and NOMEX blankets. The tiles come in three colors – each one withstanding differing amounts of heat. White tiles can withstand heat up to about 1,200ºF (650ºC), black tiles up to 2,300 F (1,260ºC) and gray tiles up to about 3,600ºF (1,649ºC). Location of tiles is determined by the amount of heat an area receives upon re-entry. White blankets made of coated Nomex felt reusable surface insulation are used on the upper payload bay doors, portions of the mid-fuselage and aft fuselage sides, portions of the upper wing surface and a portion of the OMS/RCS pods and is protective up to temperatures of 700ºF (371ºC). The shuttle TPS is reusable, and the tiles are like marshmallows made of glass—10% silica (sand) and 90% air—a marshmallow is essentially a ball of sugar puffed up with air—the TPS tiles are similar, microscopic air pockets make the glass block lighter than Styrofoam but highly resistant to heat.

In the Apollo era, capsules did not fly in the same way during return. The capsule landed with a more ballistic fall that generated heat of 5,000-6,000 ºF (2,760 ºC). The interior of the command module must be protected from the extremes of environment that will be encountered during a mission—the cold of space (c.-280ºF / -173ºC) and the heat of the direct rays of the sun (280ºF / 138 ºC), and the intense temperatures of reentry (5,000ºF / 2,760ºC). The interior remained a comfortable 70º F (21ºC).

The principal task of the heat shield that forms the outer structure is to protect the crew from the fiery heat of reentry—heat so intense that it melts most metals. The ablative material makes up the shield is a phenolic epoxy resin, a type of reinforced plastic. This material turns white hot, chars, and then flakes away, taking the heat with it. The heat is absorbed and shed by the shield and does not penetrate to the capsule interior.

The command module enters the atmosphere with its base down; this is covered by the thickest part of the heat shield. The heat shield varies in thickness from ½ to 2¾ inches thick (1.3-7 cm) and weighs about 3,000 pounds (1,360 kg).

Inform trainees that either one of these forms of TPS would be a good idea for their challenge.

Conduction, Convection, Radiation: Tell the trainees that they will be designing a Thermal Protection System of their own, but before they do, they should know a few things about how heat and thermal protections systems work. Review definitions of:

Conduction: Heat travels through Solids by conduction. Some objects are better conductors of heat than others. During the design challenge, more contact between objects means more heat transfer through conduction.

One example of conduction is accidentally leaving a metal spoon in a pot of boiling soup—while initially cool to the touch, the handle can burn you if the heat is allowed to travel up the length of the spoon.

Convection: Heat moves through Fluids through convection. “Fluids” means any matter that conforms to the shape of its container—(liquids and gasses, like water or air). As the fluid warms, it expands—the same mass now takes up a greater volume—meaning it becomes less dense. The warmer, less dense material rises or floats to the top of the fluid and the denser, cooler fluid moves down to take its place. During the challenge, convection can help to carry heat away.

These convection currents are responsible for weather patterns and are how hot air balloons function. As a side note, convection cannot happen in microgravity. Without gravity nothing rises or sinks, regardless of relative density. Special fans are required to cool computer equipment and to warm food, as air of different temperatures will not circulate on its own.

Radiation: Heat also travels in waves, or through radiation. Radiant energy (like from a radiator) is how energy from the sun warms the Earth despite the 93 million miles of the vacuum of space that lie in between.

·  If you are near a hot object and you touch it and get burned, that is Conduction.

·  If you feel the warm air currents rising from it, that is Convection.

·  If you are near enough to the heat source to feel the warmth on your skin, even though the air is still, that is Radiation.

·  Activity (40-45 min)

Tell the trainees that they will be building a thermal protection system out of the materials available on the table. Pick up one of each material and hold it for trainees to see and name it. All materials are already cut to size except the yarn. The abilities of each design will be tested with the blowtorch.

The trainees’ shields can be no thicker than a standard pencil: ¼” (7 mm.). An easy way to test this is to see if the shield will fit under a ruler balanced on two pencils. Each shield will be secured to the test stand and a raw egg placed behind it on the stand. The shields will be subjected to 3-5 minutes of heat from the blow torch. Eggs will then be removed from the stand and cracked to see how much damage was done by the heat.

Give students their data sheet, and explain that trainees have a budget of 100 credits to purchase materials. They will be responsible for keeping track of what was spent on the data sheet. Left-over credits will apply to their score, but they should build with the intent of protecting the egg. Have them tally their remaining points.

·  Testing (30 min)

Take trainees outside to test their TPS. Place eggs and TPS, time for 3-5 minutes. When eggs are cool, crack all and check the interior. See data sheet for scoring. Have each group report on what materials they used and how they believe the TPS they built will work, and complete their data sheet during testing. Discuss what worked and what did not as tests commence.

·  Closing (20 min)

Chart all of the teams’ data on a poster or spreadsheet. Review the 3 methods heat can be transferred. Review how NASA protected capsules and space shuttles. Review what items seem to work best with heat shields. After the team has left, clean up the activity and pack up supplies.

Additional Activity Notes:

·  Safety Notes:

Be sure to set the orange cones to keep trainees back.

NEVER burn TPS indoors.

In care of rain, stands can be set up under overhangs.

If there is lightning, the trials should not be done until weather clears.

·  Additional Demo Option:

You can allow each work group to select one material, and one at a time in test stand and burn so that trainees can see how some materials will respond to heat and fire before building their shields.

References and Revision History:

•  Boeing employees: Carista Brake and Jason Powell

•  Melissa Snider

•  Mary Mast

•  From Julie Clift, Earth to Orbit http://edc.nasa.gov/

•  Jason Jirsa. Education Specialist, USSRC. 2005.

•  2015 update for Space Academy for Educators: Andrea Tribo