&p_a=It begins with A:
ONE WORD: A being or creature from outer space; an estraterrestrial
&p_b=Both words begin with B:
TWO WORDS: A theory stating that the universe began as a tiny but powerful explosion of space-time roughly 13.7 billion years ago.
&p_c=Both words begin with C:
TWO WORDS: The geographical region from which many USA spacecrafts have been launched
&p_d=It has D:
A white or gray mass of particles of water or ice in the air
&p_e=It has to Es:
A meteor that has fallen to Earth.
&p_f=It begins with F:
A reaction in which an atom's nucleus is broken apart, releasing a tremendous amount of energy. It is used in many power plants on Earth and is in atomic weapons.
&p_g=It begins with G:
ACRONYM: Global Positioning System.
&p_h=It begins with H:
ONE WORD: One of the 18 moons of Saturn, the largest-known irregular-shaped body in our Solar System. It has a variable rotational period. Craters mark the surface. 
&p_i=It begins with I:
ONE WORD: The solid form of water, frozen water.
&p_j=It begins with J:
ONE WORD: The largest of the planets and the fifth from the sun. It has 16 satellites and is surrounded by a transient planar ring system consisting of dust particles. 
&p_k=It has K:
A space capsule or vehicle put into orbit.
&p_l=It begins with L:
ONE WORD: The first dog sent into orbit around the Earth. 
&p_m=First word begins with M:
TWO WORDS: A temporary perturbation (disruption) of the Earth's magnetic field, caused by solar flares, which eject plasma from the Sun's chromosphere..
&p_n=It begins with N:
ACRONYM: ational Aeronautics and Space Administration.
&p_nn=NO WORDS:
No words in English that contain Ñ.
&p_o=It begins with O: 
ONE WORD: When a smaller astronomical body passes behind a larger astronomical body (entirely obscuring its view).
&p_p=It begins with P:
ONE WORD: The layer of the Sun which is visible to us. 
&p_q=It has Q:
ONE WORD: An imaginary line that is thought of as circling the earth and is the same distance from the North Pole and South Pole.
&p_r=It begins with R:
An imaginary line that is thought of as circling the earth and is the same distance from the North Pole and South Pole.
&p_s=It begins with S:
ONE WORD: Objects that orbit a planet or a moon. Many man-made satellites and one natural satellite (the Moon) orbit the Earth.
&p_t=It begins with T:
ONE WORD: A constellation of the zodiac also known as the Bull. This constellation is seen along the ecliptic between Aries and Gemini.
&p_u=It begins with U:
ACRONYM: Unidentified Flying Object.
&p_v=It begins with V:
ONE WORD: A space entirely empty of matter.
&p_w=It begins with W:
ONE WORD: The state in which an object appears to have no weight but the object's mass remains the same. During it, an object's gravitational pull is negligible (close to zero).
&p_x=It has X:
A large system of stars separated from similar systems by vast regions of space.
&p_y=It has Y:
ONE WORD: The scientific study of space, including the planets, stars, galaxies, comets, and nebulae.
&p_z=First word begins with Z:
TWO WORDS: A star at the eastern end of Orion's belt (in the constellation Orion). It is also known as Alnitah. A form of oxygen, O3, produced when ultraviolet light passes through air or oxygen.

&r_a=ALIEN
&r_b=BIG BANG
&r_c=CAPE CANAVERAL
&r_d=CLOUD
&r_e=METEORITE
&r_f=FISSION
&r_g=GPS
&r_h=HYPERION
&r_i=ICE
&r_j=JUPITER
&r_k=ROCKET
&r_l=LAIKA
&r_m=MAGNETISM
&r_n=NASA
&r_nn=NOT A WORD
&r_o=OCCULTATION
&r_p=PHOTOSPHERE
&r_q=EQUATOR
&r_r=RADAR
&r_s=SATELLITE
&r_t=TAURUS
&r_u=UFO
&r_v=VACUUM
&r_w=WEIGHTLESSNESS
&r_x=GALAXY
&r_y=ASTRONOMY
&r_z=ZETA ORIONIS