2 letters:
2d, go, in

3 letters:
2nd, far, gap, jut, key, nro, off, out, pad, run, sac, sky, van, way

4 letters:
away, cosy, cozy, cram, deep, door, dust, fill, hair, hard, hold, hole, inch, last, lead, line, loft, near, next, nigh, open, over, park, pass, play, room, sack, seat, snug, take, usaf, void, wall, wide

5 letters:
angle, attic, blaze, braun, cabin, cache, chaos, clear, close, cover, craft, ether, event, field, first, flies, force, no-go, paint, place, point, pouch, press, roomy, solid, swath, touch, wagon, wedge

6 letters:
aether, annual, areola, beyond, broken, cavern, cavity, cellar, closet, cosmic, crenel, cut in, extend, filler, flight, fornix, garret, hollow, indent, lander, launch, length, locate, locule, margin, matter, metric, nearer, nebula, occupy, period, plasma, plenum, pocket, remote, salyut, screen, second, serosa, skylab, sphere, spread, stacks, studio, sudden, thrill, travel, ubiety, usable, use up, utmost, vacuum, vector, volume, waggon, widely

7 letters:
airlock, bedside, bryales, bulwark, capsule, chamber, closely, clutter, depress, distant, doorway, edge in, edge up, expanse, far-off, faraway, farther, filling, further, get out, glottis, headway, houston, jut out, keep up, loculus, opening, parking, pioneer, precede, proceed, project, prolong, rampart, removed, spacial, spacing, spatial, squeeze, sustain, take up, vacancy, whisker

8 letters:
adjacent, airspace, air lock, avionics, back out, conquest, continue, crenelle, cupboard, dislodge, distance, epidural, facility, farthest, furthest, headroom, historic, infinite, isometry, location, overhead, poke out, position, protrude, sea room, services, spacious, starship, subspace, take out, touching, unbroken, vaporize, wardrobe

9 letters:
aerospace, air space, astrogate, attractor, audacious, bring out, circulate, clearance, cogitable, compactly, convector, countdown, crowd out, dimension, emptiness, enclosure, groupware, houseroom, immediate, indenture, launchpad, limitless, looseness, myelogram, perilymph, proximate, proximity, reach out, scattered, spaceship, spacesuit, space age, spark gap, spatially, spreading, stick out, substance, swap file, threshold, translate, treatment, uttermost, wavefront, workspace

10 letters:
agate line, black hole, cargo area, cargo deck, cleft foot, clutter up, contiguous, continuous, cosmologic, crawlspace, deep space, depression, disc space, disk space, elbow room, exobiology, go forward, hemothorax, hollowness, huntsville, interstice, ion engine, launch pad, lebensraum, null space, open order, relativity, separation, space-time, spacecraft, spatiality, spinal tap, splashdown, sponginess, swap space, terreplein, trajectory, vertically, wave front

11 letters:
aeronautics, beach wagon, biomedicine, cavity wall, coincidence, column inch, compartment, cosmic dust, cosmologist, counterglow, crawl space, directional, farthermost, force field, furthermost, gegenschein, hydrothorax, indentation, launch area, myelography, outer space, pericardial, phase space, room access, superstring, wine cellar

12 letters:
'tween decks, aeromedicine, astrobiology, astronautics, beach waggon, cosmological, dimensioning, double-space, hairsbreadth, horizontally, intermediate, interstellar, living space, space helmet, space rocket, storage area, trailer camp, trailer park, unmeasurable, visual space

13 letters:
asteroid belt, astrodynamics, between decks, discontinuous, disk overhead, electric fire, hilbert space, launching pad, noncontinuous, order bryales, parking meter, parking space, pelvic cavity, pressure suit, radius vector, space capsule, space program, space vehicle, squeezability, station wagon, storage space, uninterrupted

14 letters:
apollo program, claustrophobia, command module, double glazing, enclosed space, field of force, gemini program, hair's-breadth, intervertebral, solid geometry, space medicine, spaciotemporal, spatiotemporal, station waggon, urban planning, uterine cavity, virtual memory

15 letters:
compressibility, electric heater, euclidean space, historic period, hyaluronic acid, lumbar puncture, serous membrane, spinal puncture, virtual storage, whispering dome

16 letters:
appointment book, dynamical system, polyhedral angle, spatial property, state of the art, studio apartment

17 letters:
aviation medicine, ballistic capsule, cardiac tamponade, elliptic geometry, historical period, natural enclosure, pericardial space, peritoneal cavity, relativity theory, strange attractor, topological space

18 letters:
aerospace engineer, aerospace medicine, change of location, formatted capacity, interstellar space, magnetic resonance, pericardial cavity, sense of direction, set of bookshelves, subarachnoid space, whispering gallery

19 letters:
backspace character, epidural anesthesia, intergalactic space, interstellar medium, riemannian geometry, spatial arrangement

20 letters:
appointment calendar, epidural anaesthesia, interplanetary space, space-time continuum, theory of relativity, unformatted capacity

21 letters:
interplanetary medium

22 letters:
greater peritoneal sac

23 letters:
vestibule of the vagina